It was my impression that the things the Nobel prize is awarded (at least the more famous ones) are one's that were discovered when the recipient wasn't that old, just that the prize is awarded a considerable time after the discovery. After all, the discovery has to prove its importance and stand the test of time.

Also, and it's pure speculation — if I were a Nobel prize laureate, I'd be able to discuss professionally interesting topics with more or less whomever I'd like, live, or in private or group correspondence, instead of a public forum.