To be fair, no one has made the claim that if you only watched TDS and TCR, you'd be "well informed". The case has been made that if you only watched those shows, you'd be better informed than if you only watched Cable News -- which is a far cry from being "well informed", but not a far cry from the truth. That's the whole point: Stewart and Colbert do a better job in their four hours of television a week informing the public than any other four hours of cable news do.

I would argue that Stewart and Colbert's audience generally gets its news from the Interweb. Perhaps the Comedy Central shows are the only place on TV where they get their news.

I certainly wouldn't say that those that watch only television news are all that "well-informed" either. I think the only places you can get really informed are NPR (which gets far higher ratings than all the right-wing hatefests) and PBS, and to a lesser degree newspapers like NYTimes and Washington Post.