I posted another survey dealing with this, yes. This one is just more detailed and has some interesting factoids. I personally didn't expect that there would be so many American Catholics self-identifying as 'progressive.'
Why not? At least according to most surveys that I've seen in the recent past, Catholics have been roughly on par with or slightly to the left of America as a whole for a while now. (In the more distant past they were obviously a strongly partisan Democratic group but not really a strongly ideological 'progressive' or 'liberal' one in the sense that more recent surveys usually purport to measure.)
I don't deny that a significant number of American Catholics differ with official church teachings, I'm just a tad surprised that mainline Protestants don't outnumber them, what with the increasing number of Protestant churches adopting moderate-to-liberal political stances.
To be fair, though, this article isn't specific about what churches these mainline Protestants are affiliated with, so I suppose that has to be considered as well.
Mainlines as defined in the media can be a pretty broad range. Let's not forget that UMC member George W. Bush could be considered a mainline Protestant.