How would Mittens get rid of Obamacare when it was modeled after Romneycare? I don't think Paul's head is even in that game. And I don't think I've heard Huntsman mention it.
Basically, he has used the Tenth Amendment argument: "We may have done that in Massachusetts, but it should not be imposed on the states by the federal government." Whether or not he would then act to get rid of Obamacare, that is the question, but he has said he is against it.
On a number of points with Romney, he is saying the right things now--he talks a good game--but there are legitimate doubts about whether he would follow through.