Why?
Iowa has few delegates, and only 50% of the time does the GOP winner go on to get the nomination. It really is meaningless for the GOP (it is a great predictor for Democrats, though).
New Hampshire’s record isn’t much better. McCain won in 2000, Buchannan in 1996. Plus, Romney is pouring money into New Hampshire.
Cain just needs a good showing in these states, and I think he’ll do that if leading in the national polls.
Cain’s breakout should come in Florida and Carolina.
You are totally right in the importance of NH and IA in a normal cycle, but things are so volatile right now that a big win somewhere early would get the momentum started.
Perry is still alive and Newt is slowly gaining steam. And let’s not forget Mittens. Any one of these dudes could do something surprising and lock this thing up right away. GOP Primary voters generally coalesce around the best shot. I can’t remember another GOP Primary election where things drug out like the Rats in ‘08.