Ratings for Daily Show and Colbert: source.
Setting aside the fact that polls of the nation show large support for healthcare reform, these television ratings are bogus.
If you'll notice, there are some minor differences in the titles of the shows compared to what they're normally called. "A" Daily Show and The Colber"T" Repor"T". These names come from during the Writers Guild Strike, when Viacom forced these shows back on the air despite not having writers. In a show of solidarity, both Jon Stewart and Stephen Colbert changed the names to emphasize the fact that these are not the quality shows people should expect with their brilliant team of writers. Most of the shows were heavily ad-libbed, and while funny, they resorted to a fake feud with Conan O'Brien just to fill time on all three shows. Ratings would be quite noticeably down during this time. I'm not sure when a representative time would be, but an average over a year or two would probably be better, and I would pick a year without an election or a writer's strike on TDS, TCR {iand[/i] O'Reilly and compare apples to apples.
I still think Fox is going to have higher ratings...but there are probably more than a few liberals who watch Fox for the reality show drama of it rather than because they actually agree with it.