Maybe David Letterman can get Mario Vazquez to reveal what prompted him to quit American Idol. The Latin warbler will appear on tonight's Late Show with David Letterman to present the Top Ten List, CBS confirms. Meanwhile, Vazquez seems to be backing off his initial claim that he left the show to "take care of some personal issues with my family," telling Access Hollywood that "of course something did happen" to him since Idol began, "but that will stay personal." It's Paula's damn good-luck charms. They're cursed!