Actually, I think Cain has a better chance at beating Obama than your average New York mayor. And a Mass Governor? That's a failed state already. Candidates from there are not to be taken seriously.
Of course, Cain could beat Obama if he could win the GOP nomination, but he can't. The two parties have nominated 50 candidates since 1912. All but four were Presidents, Vice Presidents, Governors or Senators. One of those was General of the Armies Dwight D. Eisenhower (a special case). Two others (J.W. Davis in ‘24 and Wendell Wilke in ‘40) were desperate, last resort selections neither of whom won a general election. The fourth was a long-serving Cabinet Secretary and celebrated do-gooder named Herbert Hoover. He turned out to be he most inept politician ever to occupy the Oval Office (before 2009).
Political neophytes occasionally run for President. They never win. It just doesn't work that way, and for good reason. The presidency is a job for a skilled professional politician, voters understand that and obviously unqualified applicants get rejected early in the process.
That's reality and it isn't going to change miraculously for the convenience of Herman Cain and a few delusional Freepers.