(1) It simply is untrue that Romney is not winning conservatives. In fact, a super-majority of Romney voters are in fact conservative and he has won more conservatives than any other candidate. The most conservative voters are not the bulk of his coalition, for sure, but overall his support is coming from the right side of the political spectrum.
(2) The Romney coalition in 2012 is more moderate than the Romney 2008 coalition was. In most of the early contests – at least outside the South – Romney secured the support of very conservative voters four years ago. That is not the case this time around, not nearly to the same extent. Even so, his coalition in 2012 is a hybrid of the McCain ’08 and Romney ’08 vote.
(3) This is a virtually unbeatable coalition, if he can maintain it. Romney has basically situated himself exactly in the middle of the GOP electorate: a plurality of his voters are somewhat conservative, with the remaining sampling from the moderates and the very conservatives. To defeat this coalition, an opponent would have to either steal some of his very conservative voters or cobble together a coalition that includes the far left and the far right of the electorate. Either would be a very difficult task to accomplish.