[dpcan]

What about the simple fact that if I’m not going to the blog’s website directly, I’m not seeing or clicking on the Google adsense ads they were displaying?

Or that you weren’t typing the name of the blog into Google to find it each time, and potentially clicking a sponsored link?

The whole idea of reader hurt Google’s business model.

[jdechko]

Or, it’s a highly customized list of websites and interests that is tied to an individual user, and therefore can be advertised against.

Google could have put ads in Reader if they wanted to.