In fact, the remarkable thing about abortion is precisely how steady public opinion has been on it for many, many years. Perhaps this in and of itself is interesting — as Ross Douthat pointed out, there is some decent evidence that Gen Y’ers are less inclined to take the pro-choice position than Gen X’ers or Baby Boomers — although they are still more pro-choice than the voters they are gradually replacing in the voting pool, which are members of the Silent Generation. This is in spite of the fact that young Americans are considerably more liberal than their peers on issues like gay marriage and marijuana legalization, issues on which there is more tangible evidence of “momentum” in favor of the liberal position. There are evidently an increasing number of pro-life, pro-gay marriage Americans, particularly among Generation Yers, a position it would have been very unusual to encounter just a few years ago.
There’s some interesting discussion in the comments as to how this could be.