Santorum is talking about gaming the tax rates to give preferences, and supports more government intervention in the economy, and Newt angered a lot of conservatives with his attacks on Bain Capital. By default, they've left Romney as the rhetorical defender of capitalism, except for his stance on RomneyCare.
That's more of a pathetic commentary on the stupid things said by Newt and Santorum than it is anything good about Romney.
Romney remains the same slimy gameshow host he's always been, but these other guys aren't helping themselves in taking advantage of that. I'm still pulling for Newt, though, because I think he is the only one of the three serious contenders capable of framing the free market v. socialism debate in a manner appealing to swing voters.