The Putnam competition, in spite of being six hours long, is severely time limited: Each year, there are probably hundreds of people who could solve all 12 questions if only they had enough time, but only six people who manage to answer more than 8 or 9 questions within the time limit.
If you're going to solve Putnam questions in an average of 30 minutes or less (including carefully writing out the solutions) the only way to do it is by having flashes of insight. Working hard doesn't help, because there isn't enough time to work hard. Putnam winners are people who successfully apply Feynman's algorithm for problem solving: 1. Write down the problem. 2. Think hard. 3. Write down the answer. (Feynman, incidentally, was one of the first Putnam fellows.)
For a competition which is theoretically about mathematics, a shockingly large number of Putnam Fellows end up moving to a different field. I think this is the reason why: Mathematics is a very old field, where it's very hard to do anything without working hard. Putnam fellows by their nature tend to seek the instant gratification of finding simple and beautiful solutions to problems -- and so we're drawn away from mathematics and into more immature fields like computing.
Yes, Putnam fellows are smart -- but we're no more disposed towards hard work than anyone else.
For most people (atleast that I have observed), becoming independent really focused them and helped raise thier game and productivity^.
Nothing is as motivating as neccessity?
^n.b. not applicable to Putnam winners ;-)