It took over seven minutes for David Letterman to NOT apologize.
Although Letterman claims that he joking about 18 year old Bristol Palin having sex at Yankee Stadium when he said that "during the seventh inning stretch she was knocked up by Sarah Palin" - Bristol Palin wasn't there. 14 year old Willow Palin was there.
My guess is that a writer got the two daughters mixed up.
So....why not just apologize?
Because David Letterman used the controversy over statutory rape as another joke proving to the world that he has no class.