I semi-agree. I think Carson did go for politics, but it was much more of a "joke about whoever's in power," so yeah, he hit Reagan hard and Carter before him, but he also hit Tip O'Neill and others, and would also happily just go after whatever was in the news in the '80s (Zsa Zsa, etc). It wasn't partisan, but there were still folks griping (from both sides) about his attacks.

Letterman, though, really did avoid most of the politics (his show being an hour later made a huge difference).

And I'm not shocked that an article from the Harvard student newspaper fails to mention ratings (or even any real facts).