Heavily implicit in your post is that the deciding factor in running is "Can I win?" That's arguably the biggest problem with our governmental process...
As for Obama...gee, he said he wouldn finish his Senate term, now he's not keeping his promise. That would make him...a politician? Seriously, I wouldn't hold it against him (if he were my Senator, I might feel differently), as it simply sets him equal to everyone else. It would be nice, though, if just one elected official kept a promise just once.