Some critics have a problem with the Late Show audience laughing and applauding David Letterman's announcement that he had sex with female members of his staff.
From personal experience, I can tell you Dave's audience is essentially brow-beaten before the show by "Worldwide Pants" interns to laugh loudly at anything he says or does. When I attended a taping last year, the crew told us plainly that if we didn't laugh loudly enough, Dave would hold back his "A" material. (Ever wonder why every bit kills on the show?)