Letterman went through the same thing in the early 90s when he moved from the 12:30 slot to 11:30. Letterman's NBC show was more groundbreaking than Conan's. But Letterman changed from the casual guy, who spray painted Bryant Gumbel's ankles, when he moved to CBS.

Conan may be more compelled than Letterman to conform because, unlike Letterman, who created a new show at CBS, Conan will be moving to an established institution in the Tonight Show, whose history goes back to the early 50s with Steve Allen and the 60s with Jack Paar. The show really reached iconic heights with Johnny Carson, perhaps the largest figure in television entertainment history.

The show is a fixture, and while Conan, like Leno, will certainly add his personal comedic talents to it, NBC will certainly expect him to conform to the established tone and expectations of the show. While it's only an hour difference, the 11:30 PM slot has a much different audience than the 12:30 AM slot.