This observation applies to all prizes, and is articulated well from another angle by Feynman (commenting on his own Nobel prize): http://www.youtube.com/watch?v=f61KMw5zVhg
I think that Obama's prize was because of his work on nuclear weapons
http://www.washingtonpost.com/wp-dyn/content/article/2009/09...
That's one reason why I think the Nobel prize is a perversion. The set of eligible people is not one or two people. There are a lot of people who do great things and in the end, the selection is fairly arbitrary. Honoring someone for doing someone honorable is good; Conferring enormous authority to one person by granting them a prize diminishes the authority of other great people.
Take Krugman. He got a Nobel for a very very specific area of economics. He now writes on an area that was not his specific focus nor has he proven himself particularly insightful. However, if he gets in an argument with other respected economists, the general perception is, "who has the Nobel?"