The media coverage suggests network talk shows still have cachet, but the landscape has changed so dramatically that some of this buzz feels infused with nostalgia. In a culture now filled with niches, audiences are smaller across the board, and the shows taking the biggest risks are on cable. Part of the reason is that with a smaller audience, a host can assume viewers share more assumptions about a joke than would a large network audience. That’s why Mr. Colbert has been able to produce formally tricky satire with only rare instances of mass confusion.

To get a sense of how the cable-network balance of power has shifted, consider that the star no one seems to be talking about for Mr. Letterman’s job is Craig Ferguson, a network host for more than a decade who has produced a fun, freewheeling talk show that follows Mr. Letterman’s.

Image Craig Ferguson on the set of his late-night show. Credit... Lisette M. Azar/CBS

To put it bluntly, why should Mr. Colbert mess with a good thing? In our new fractured landscape, where there are more places to find funny people performing than ever, network late-night talk shows not only seem more bound to tradition than those on cable, but their focus is changing. Jimmy Fallon has earned impressive ratings in his first months as host of the “Tonight” show, and in his smooth transition to an earlier time slot, he’s proved to be an appealing performer. But listen to even his most devoted fans, and they are more apt to praise his charm or likability than his humor. No one thinks Mr. Fallon is the funniest comedian who could have been chosen to host “The Tonight Show.” But he brings different talents to the job: an ingratiating enthusiasm, some deft song and dance, and a gift for getting stars to play along.

That’s not to be underestimated, since talk shows have always been about both comedy and personality. But the focus lately seems to be tilting away from comedy. The early success of Mr. Fallon may shift the show toward the variety or even morning-show genres. In part, it’s why I think Ellen DeGeneres would make a superb replacement (although she may not want to give up her afternoon-show platform) or someone with an even more diverse skill set like Neil Patrick Harris, who has been mentioned for the Letterman job as well.