David Letterman announced that he's retiring so late in the day on Thursday that The Tonight Show had already taped and Jimmy Fallon couldn't comment on-air. So Fallon saved his Letterman tribute for Friday's episode. He opened his monologue with a joke about it, and he did his very own Top 10 list. The list of why Letterman is retiring includes "Jay Leno needs a partner for next season's Amazing Race," which is a more youthful version (thoughnot by much) of Leno's own comment about Letterman retiring on Extra: "Oh, well, you know, he and I [are] gonna do The Sunshine Boys on Broadway, so we're very excited about that." Maybe DL should stick around a little longer just to help Tonight Show hosts past, present, and future with their jokes about him.