He's a RINO loser & why should Conservatives pretend he's not.
If I may seriously answer this question, he might govern differently as president because a) America is not Massachussetts and b) he might have one or both congressional houses in Republican hands instead of Democrat hands.
I'm not under any illusion that Romney would be far less conservative than I would like but there *is* a possibility that he would govern more conservatively than he did in Massachussetts because he has a different constituency and a different congress.