Well, duh. If you were quite intelligent and talented, why would you want to get involved in the muck of politics? Or: that's because those people aren't smart/reflective enough to think about the people who might be smarter or more qualified than they are, and are able in their ignorance just to go ahead and do something. Fortinbrases all.
Or something.
Clinton went to Georgetown, was a Rhodes Scholar at Oxford and then went to Yale Law School. Presumably, he would have been exposed to some awfully darn smart people at those places, including some who were smarter than he was. I think they would qualify as the equivalent of growing up in Manhattan.
The Clinton angle to Phil's post just seems screwy to me. Clinton is, in fact, brilliant, and, as you say, knows many brilliant people.
Greenspun, however, has read Clinton's book. And from that, no brilliance shines, none whatever.
Can we be a little less psychologized about this? If you live in a small place and you're ambitious, you're likely to look for connections. Politics has historically been one of the best ways to develop connections. This is particularly so in poor areas like Arkansas, where politics has been one of the very few avenues of advancement available to poor or averagely-circumstanced white kids.
I take nothing away from Clinton's intellectual abilities. They're impressive. But he got his Rhodes because he'd managed to come to Fulbright's attention and then cultivated him. It seems a darn sight less difficult to do that in a small, poor state with a hierarchical and patronage-based cultural system (as it certainly was in Clinton's youth) than in, say, California or Ohio of that day.
Then there's the patrons' angle. In the bigger places, the people you need to cultivate have a harder time finding and supporting the brilliant, ambitious Clinton types because they have complicated systems to maintain and many obligations to pay off. They have far less patronage to spare.
And the states they have to survive in are extremely complex political systems that take a great deal of energy to keep track of, and in which they necessarily create lots of enemies who cause them problems later on. Of our post-WWII presidents, only Reagan came directly from big-state politics. The rest were either nationally prominent before they started running (Eisenhower, Johnson, Nixon, Bush I; Reagan had some of this too because of his celebrity) or came from small states (Carter, Clinton), or came out of a state with a governor so preternaturally weak he could campaign from day one for the big prize (Bush II).
The one psychological point I'm willing to concede here is that in smaller settings, people might be able to make up their minds earlier whether they're worms or glow-worms.