Yes, he's got a film to promote, but you can assume Jon Stewart will be bringing up the whole Kristen Stewart two-timing situation with Mr. Pattinson given it's his first interview since the story was spilled (in time for said film release. They'll be back together for the release of *inhales* The Twilight Saga: Breaking Dawn - Part 2).
A producer for The Daily Show said: "Rob must be a good sport to agree to it (or really under the cosh of the Cosmopolis PR team - it's being released in the US this month for some reason). US stars rarely appear on shows like this until a lengthy amount of time has passed since an embarrassing episode."
If you'd like to watch Robert hide under his eyebrows, this highly anticipated edition of The Daily Show will air "next Monday", which means it'll be on Comedy Central UK approximately 24 hours later. Which is strange as I can't see it in the listings as yet...