I have a confession to make...
I love the Daily Show (that's not the confession), I think Jon Stewart is hilarious and on the money (that's not the confession either), but I generally think most of the rest of the show sucks (that's the confession). I love it when politicians and writers are the guests, but I find actors/comedians/musicians as guests boring. And I think most of the corrospondents try to act stupid too much of the time. Jon is funny because he is smart and can point out flaws in governmental/political logic. Everyone else is just parodying news casters, by trying to act dense. Dumb and Dumber do the news. I have one wish (actually two...) more Jon, less anyone else, and bring back the couch. Is that too much to ask?
You expect too much from actors/musicians. They've never had a need to say anything meaningful or intelligent. They're kind of like supermodels in the fact that they get by with looks and/or fame, that suffices enough to not require them to make any sort of conversation.
And there are moments when I get annoyed with the correspondents.
But sometimes, I think they're fantastic. I think acting dense is a tool that they use when dealing with dense people- like Dan Bakkedahl's piece on the guy doing the bum-vertising (though I'm biased there- I know Dan and I think he's insanely talented).
Also, on a show like this, it's hard to assign blame, when you're not really sure who did the writing, what the director said, how much input the correspondents have... y'know?
You are right, it could be the writers or the director, but either way, it's getting tired.