Answer: Serving in the Presidency of the United States was their first experience with Elective Office.
It's a rather uninspiring group, on the whole. But, it also points out that the election of Herman Cain would hardly be unprecedented, even in the Modern Era.
Also, I think Cain's candidacy leads to a bigger point: All the professional pols we've entrusted with the office ain't been so hot, either. Bill Clinton began campaigning for the Presidency the moment he got done shaking JFK's hand at Boy's State in 1962. Richard Nixon, LBJ, and both Roosevelts were chronic campaigners and office-holders. Some of our greatest Presidents held very few elective offices before becoming President (Lincoln, Madison, Reagan) others spent entire lives in office (Coolidge, Hayes, Truman). So what?
Leadership is an amorphous quality. It slithers and slides around, running into the furniture and doorposts of the times. They say Lincoln would have a tough go of it today because he had a squeaky, unimpressive voice. And yet, George H.W. Bush would hardly have had a chance in the old days because his voice was soft. Again: So what?
If there was ever a time when America needs a leader from outside the paradigm of the colossal, titanic, herculean disaster of Federal (elective?) Government, it is Now, Today. Is it Herman Cain? I don't know, but to dismiss him as some sort of "amateur" is ironic in the extreme, when you consider a man with a very impressive background in ballistics, finance and upper management is an "amateur", but Bill Clinton was a "professional".
One of the tricks to finding the missing piece of the jigsaw puzzle, is to get up from pouring over the thing, rub your eyes, and walk away. Then, come back a while later with fresh eyes, and shazam, there's the missing piece: Right in front of your face. The Federal Government is the biggest most disastrous jig-saw puzzle in human history, and we sure need some fresh eyes to give it a look-see.