Why does Fred have ads on his blog?
Fred Wilson (A VC) is a good friend and a terrific guy, and you really should read his blog. My guess, without seeing his bank statement lately, is that he doesn't need the income he gets from the ads on his blog.
So why do it?
Well, I just posted on the squidblog about Squidoo's experiment with AdSense. I think there's something non-obvious going on here. Magazines are better with ads, and so are many websites.
Better? I know that Fred does his ads as an experiment/handshake with the firms he knows or is interested in. But for many sites, it turns out that sites with good ads ("Anticipated, personal and relevant" as I wrote eight years ago) actually give users more confidence and meaning.
In other words, even if you never cashed the checks from Google, you'd come out ahead. (Your mileage may vary, natch).