Have you ever clicked on an ad that was embedded in an RSS feed? Ever? I never have. In general, the kinds of people who use Readers are pretty good at filtering - at using technology that does it for us, and at having cognitive strategies that let us sort what we actually see. We're not the kind of people advertisers dream about. Advertising relies on being able to redirect attention, and (usually) cause us to make irrational decisions.
And now Google Reader is gone. I imagine that over the next few years, we're going to lose a lot more free, ad-supported services that we good-filterers, high-information users enjoy, because we're terrible advertisees. I still haven't paid for Newsblur but I think the days of free, high-information (not data-intensive) services will soon be past.