It's not because of 9-9-9, which has some problems - the chief of which is, it's regressive. Michele Bachmann, with whom I am not impressed, highlighted those problems in the recent debate. But Cain brings to the table something that no one else does:
1. He is a man who rose from segregation and discrimination to become a CEO (unlike our current president, who grew up in middle class, culturally diverse Hawaii and experienced minimal discrimination). In short - and I hate to put it this way, but it's true - but Cain's a more authentic African-American than our President. There are very few African-Americans like President Obama, but millions of African-Americans who grew up the way Herman Cain did.
2. Cain's 9-9-9 plan at least acknowledges something that no other candidate does: that the tax system is broken in this country and needs to be torn down and re-constituted. Again, 9-9-9 is not necessarily the answer - but it's PART of the answer, and he's the only candidate who is willing to do something bold to reform a an inefficient tax system with perverse incentives that penalize strivers and reward the well-connected.
If he and Mitt Romney can get together on this one issue - and I'm not optimistic that they can - the Romney-Cain ticket could be pretty formidable.