Stewart is playing a completely different game than either Colbert or Limbaugh. He's more the court jester, a role he's playing brilliantly. In fact he's playing it so well that he's picked up more credibility than his favorite targets: the media and the politicians.
I'd contest that. I don't find him remotely funny as much as I do profoundly irritating. But not as irritating as his fans.
A lot of folks miss the point with Stewart. That includes some of his fans. Stewart is generally annoyed by the sheer level of BS out there from both the Media and the Politicians, on both sides of the fence. Stewart's humor only works if you too appreciate just how ridiculous CNN, Fox, MSNBC, the DNC, and the GOP truly are. I think I've seen Stewart tell maybe one funny joke that wasn't tied to current events in my life, and I've never seen Stewart actually be funny in film. All his movie roles suck.
The guy is a great one to watch when he personally gets interviewed, and he's probably one of the better interviewers out there. The Daily Show is aboslutely hillarious during the first watch because you're on the same page as it, but if you go back and watch old clips, they don't stand up well. It's not a sketch comedy show, it's commentary. Hillarious commentary.
I really don't know what Rush Limbaugh you're listening too, but you obviously get a totally different take from the show than I do. Rush does an excellent job of handling kooks from both sides of the argument. Colbert plays at being the kook trying to appear sane, and will continue to be successful at this act as long as the parody remains entertaining. Rush on the other hand is entertaining not as an end, but as a method of delivering his message. Colbert, the buffoonery IS the message, and face it, shit chucking monkeys have only a limited appeal and lifespan.
Limbaugh thrives on the outrage, and will say and do stuff to intentionally provoke that. I'm specifically thinking of his song parodies that are waaaaaayyyyyyyyyyyy over the top often. Limbaugh's game is more challenging than Colbert's because Limbaugh lets callers on. Sneardly does a pretty solid job filtering out the Right Wing Wackos, but it's when they do get past him that you get to see the fact that Rush himself isn't nearly as extreme as the stuff he's saying.
Part of the genius of Colbert is that while he's playing the game in a "safer" way than Limbaugh, he's also done a very good job avoiding the easy path, which would be a single note parody. Instead he is incorporating a more layered approach. Colbert has found ways to lampoon hollywood, DC, Wikipedia, Religion, Democrats, etc. If we didn't have is past as a Daily Show consultant to clue us in to the "real" Colbert, I suspect that it'd be a lot harder to pick out what was real and what was showmanshp on his part. He's built up a pretty amazing stage personality.
Limbaugh of course is the better of the two as he's been at this for a while and still manages to hoodwink the sheeple that think he's actually serious about the stuff he's saying. But Colbert's the only other guy that can come close to his level of showmanship.