I think you underestimate how many people are vested in that they voted for that nice black man—and don’t want to give up their big pile of open-minded, tolerance chips for some Southern white guy who talks about God and guns and so, they presume, is a bigot.
Anyone that stupid would consider all Republicans bigots, even Herman Cain. There’s no sense trying to appease them and, in the process, alienate the base. That’s seems to be exactly what Romney is doing now.