- There's no crowdwork. In a lot of ways, it's more theater than standup routine. They're playing to the cameras (or mics), not the people. It's not about calling the room, thinking quickly, or being in the moment. It's about delivering your set.
- The sets are long. A killer 30+ minute set is totally different than a 5 minute one. When you've got an hour, there's a lot more space to relax, tell stories, etc. New jack comics need to be able to bring it in a hurry.
- The people in the audience are already fans. Making a room of people who already like you laugh is a hell of a lot different (and easier) than making strangers laugh. You don't have to establish a persona and win them over 'cuz they're already there.
- The audience has been primed. They're juiced by the setting, the opening acts, the lights, the producer telling them to whoop it up, and all that crap. Heck, the Tonight Show audience even laughs at Jay Leno's monologue so there's obviously some sort of reality distortion field going on.
- There's no bombing. The comic is doing a set that he knows works for an audience that he knows will laugh. There's no randomness at play. That's a totally different equation than new comic + new material where you need to poke around and take a chance on failing.
No doubt, soaking in albums/specials by Chappelle, Rock, Martin, etc. is valuable for any comic. But if you stop there, you're studying a fantasy.
To see what I mean, compare one of Mitch Hedberg's bootlegged concerts to one of his albums. In the bootlegs, there's a lot more dialogue with the audience. There's more wandering. There's more spontaneity. Or watch Zach Galifianakis' "Live at the Purple Onion," a live concert that shows less fantasy and more reality. The way he works the audience is what you don't get on HBO.
Watching a great comic work live is a whole different education than watching him in tv-land. You see how they weave, try new material, handle a chatty audience member, etc.