1. Republicans are barely paying attention to the GOP primaries right now, unless their state's vote is coming up soon. So there's no way Independents or Democrats — except political fanatics like us — are paying any attention right now. This means they are all voting on name recognition alone right now.
2. Based on the name recognition voting factor in #1 above, and on Gingrich's looks, anyone under about 40 yrs old doesn't really know anything about Newt Gingrich, so they don't know to vote FOR him. Thus, in the head-to-head contest, they are voting for Obama based solely on who they know more about and on Obama’s looks vs. Gingrich's looks. Gingrich is an old white guy with white hair that they know nothing about. Whereas Romney is “the right age” white guy, and they may know he's not extreme Right (aka moderate), so he's an acceptable not-Obama vote.
3. The elderly remember Newt from his days as Speaker. They may hold negative memories about him, and they haven't updated their impression of him with current information. Given time — time to get to know the new Newt, by watching current debates, and realizing that Gingrich has matured in his political positions and actions — elderly voters will come on board with Newt.
4. Once the choice truly becomes a choice of Obama or not-Obama, a LOT of people will vote for Newt. Even if they don't particularly like him, they will come to understand he is better than another 4 years of Obama.
I'm not worried about current polls that show Romney doing better against Obama than Gingrich. They simply haven't had time to learn anything about Gingrich. None of my friends know anything about Gingrich unless they are political junkies like I am. (We live in a state with a late primary, and NO ONE here is watching the debates or paying any attention to the process at this point.)
Don't worry, if Gingrich is the nominee, Obama's goon squad, with the MSM cooperating, will make sure everyone knows everything about Gingrich, and they won't have to make up anything.