Mitt Romney has a long, long history of chameleon politicking, as this article from February 2007 demonstrates (and there are plenty more to choose from).
Once again, in 2012, his views on abortion have a lot more to do with salesmanship than conviction.
Most of the evidence suggests that left to himself, Romney is moderate on abortion; but there can be absolutely no confidence in his ability to withstand pressure from interest groups of any variety. Romney will simply be whatever his political bosses want him to be. He has no clear vision of his own.
The good news? Republicans are getting the message: Extreme social conservatism is unpopular. It has to be covered up if you want to win elections; and guys, in the long run, it just isn't worth it.