From VN's Olympic selections article:
Leipheimer punched his ticket to Beijing by finishing in the top three overall at last year’s Tour de France, while Hincapie qualified by taking second in the time trial at the 2007 Tour of Benelux.
I'm having trouble picturing the USOC folks sitting around thinking of how to pick the best cyclists. "Tour de France? Yeah, if someone takes top three, I think he gets a spot. Also, don't overlook the Tour de Benelux time trial, that's where true champions show their colors."
Or something like that.