Can you please elaborate on why the originals were replaced and how the replacements are better?
I started to post a response, but then I realized that it was getting much, much too long for a comment, so I am going to post it here.
[Warning: serious liturgical minutia ahead.]
First off, I should clarify that I had nothing to do with the composition of the RA Haggdah, nor do I know anyone involved with the project, so I can only guess at the reasons for the changes. Second, I wouldn't go so far as to say that the RA's version is "better" than the traditional version; it's a matter of the purpose of this particular Haggadah. I presume that where choices were made, the goal was to produce a text that is accessible, thought-provoking, and relevant to contemporary Conservative Jews.
Now for the details. As far as I can tell, they begin with the midrashic exegesis of Deuteronomy 26:5-8. The RA Haggadah begins by quoting the entire passage, which I think makes the text a bit easier to follow. It skips the initial interpretation of ארמי אבד אבי, which states that Laban the Aramean was worse than Pharaoh, because he attempted to destroy all of Israel (via Jacob) rather than Pharaoh alone. I would imagine that this was omitted because it requires a strong familiarity with Genesis to appreciate, and because it's difficult to figure out what relevant message to take from it. However, my theory is undermined by the fact that this interpretation does appear in the commentary; it is simply absent from the Hebrew text and translation. Maybe the editors set a word limit for this part of the Haggadah?
The second change is a simple expansion. The traditional Haggadah comments on וירד מצרימה, "he [Jacob] went down to Egypt," with אנוס על פי הדיבור, "he was compelled by the [divine] word." The RA Haggadah adds a quotation from Genesis 15:13 to explain that Jacob's descent to Egypt was a fulfillment of God's statement to Abraham.
To my great sadness, the RA Haggdah skips the comment on ורב, which comes from Ezekiel 16:7,6. The passage is not at all family friendly, and its relevance to the verse in Deuteronomy is rather obscure, so I think I understand why it was omitted, but I miss it. (I'm planning to compensate this year by giving a shiur on it on Shabbat Chol Ha-Mo`ed.)
The next change is somewhat interesting. On וירעו אתנו המצרים, "the Egyptians dealt harsly with us," the traditional Haggadah comments, "as it is said, 'Come, let us deal cunningly with them, lest they multiply, and if it should come to pass that a war should occur, they too will join our enemies, and fight against us, and go up out of the land'" (Exodus 1:10). On the surface, it isn't clear how the verse from Exodus serves as an interpretation of the verse from Deuteronomy. The RA Haggadah explains: "They made us appear to be bad (וירעו אתנו), for it is written that Pharaoh said to his people, 'Behold, the Israelites are too many and too mighty for us. Come, let us deal cunningly with them...'" It also adds another intepretation (דבר אחר): "They were ungrateful, for they paid back in evil the kindness that Joseph had done for them, as it is written, 'A new king arose over Mitzrayim* who did not know Joseph' (Exodus 1:8). He acted as if he did not know Joseph." In this case, I think that the RA version is not only easier to understand, but also provides more to chew on. This latter midrash is the first of a series of RA additions that present the Egyptians and Israelites as archetypes of evil and good, respectively. This presentation is somewhat problematic from a contemporary perspective, but it comes straight from the midrashic tradition, and I guess the editors saw it as an opportunity to include some moral lessons.
On ויתנו עלינו עבודה קשה, "and they imposed hard labor on us," the traditional Haggadah simply quotes Exodus 1:13: "And Egypt made the children of Israel serve with rigor." The RA Haggadah offers a midrashic interpretation: "They would impose a difficult task upon the weak and an easy task on the strong, a light burden upon the young and a heavy burden upon the old. This was work without end and futile, for the Egyptians wanted not only to enslave them but also to break their spirit."
On ונצעק אל ה אלהי אבתינו, "and we cried out to the Lord, God of our ancestors," the RA Haggadah adds a comment on "God of our ancestors:" "Because of the merit of the ancestors, we were redeemed from Mitzrayim. As it is written, 'God heard their moaning, and recalled his covenant with Abraham, with Isaac and with Jacob."
On וירא,"and [God] saw," the RA Haggadah adds, "what did He see? He saw that the Israelites had compassion for each other. When one of them finished his quota of bricks, he would help others."
On את ענינו, "our affliction," the traditional Haggadah explains, "this refers to the separation of husbands and wives" [my paraphrase]. The RA Haggadah adds a midrash about how the Israelite women ensured that procreation continued by bringing their husbands warm food and drink while they were in the fields and by offering them comfort and encouragement. It seems clear to me that this is mainly an attempt to include women in the Haggadah, but it's kind of nice and it works.
On ואת עמלינו, "and our burden," the traditional Haggadah comments, "this refers to the sons, as it is said, 'every son that is born you shall cast into the river, and every daughter you shall save.' The RA Haggadah adds the midrash that the Israelites continued to circumcise their sons even though they knew that they would die shortly after birth.
On ואת לחצינו, "and our oppression," the traditional Haggadah reads, "this refers to the force used, as it is said, 'and I have also seen the oppression with which Egypt oppresses them'" (Exodus 3:9). The RA Haggadah reads, "this refers to the straw. For Pharaoh decreed, 'you shall no longer provide the people with straw for making bricks; let them go and gather straw for themselves (Exodus 5:7). Whenever the Egyptians counted the bricks and found the quota unfilled, the Israelite overseers refused to deliver their fellow Israelites to teh Egyptians. Instead, they submitted themselves, and willingly suffered punishment in order to lighten the ordeal of the Israelites."
On ביד חזקה, "with a mighty hand," the traditional Haggadah comments, "this refers to the cattle plague(דבר), as it is said, 'Behold the hand of Adonai will be on the field..." On ובזרוע נטויה, "and with an outstretched arm," it reads, "this refers to the sword, as it is said, 'and a drawn sword was in his hand, stretched out over Jerusalem'" (1 Chronicles 21:16). The RA replaces these comments with something more accessible: "When the Egyptians made the life of our ancestors bitter, the Holy One said, 'I will redeem them,' as it is written, 'I will free you from the burdens of the Egyptians, and I will deliver you from their bondage. I will redeem you with an outstretched arm and through extraordinary judgments. I will take you to be My people, and I will be your God. And you shall know that I, Adonai, am your God'" (Exodus 6:6-7).
On ובאתות, "and with signs," the RA Haggadah includes the interpretation in the traditional Haggadah, which refers to Moses' staff, and adds another: "This refers to God's commandments. For they are an eternal sign that God saves and redeems, and a remembrance for all generations of the covenant between the Holy One and His people. Thus it is written, 'And this shall serve you as a sign on your hand, and as a symbol on your forehead -- in order that the teachings of Adonai may be in your mouth -- that with a mighty hand Adonai freed you from Mitzrayim'" (Exodus 13:9).
The next change is quite small, and it may be based on a variant text. On the word ובמפתים, "and with wonders," the traditional Haggadah reads, "this refers to the blood, as it said, 'and I will show wonders in the heavens and on the earth, blood and fire and columns of smoke'" (Joel 3:3). In place of "this refers to the blood," the RA Haggadah reads, "this refers to the plagues."
After this, the traditional Haggadah includes a sort of rabbinic math competition, in which the number of plagues is inflated from ten to 300. This entire section is omitted in the RA Haggadah, presumably because it seems like too much reveling in others' misery (and because, my God, they made maggid long enough already!).
Now that I've gone through all of this in detail, I realize that the RA's Haggadah Committee is more like me than I thought: they added a lot more text than they removed. All the more reason to create my flexible fantasy version.
*The RA Haggadah uses the transliteration "Mitzrayim" rather than "Egypt" in order to emphasize the symbolic significance of the Israelite place of enslavement rather than the actual location. Kind of silly? Maybe, but I can see why they made that decision.