How bad can Google Blog Search possibly be?

Google has a wildly popular feed reader. And they presumably know a thing or two about ranking algorithms. Why not rank blog search results based on subscribership? Or, since they’ve surely already thought of something as groundbreaking as my previous idea, maybe up that weight a tad? Would this not do away with the vast majority of spam in blog search results? Or, are the sploggers in control of massive numbers of Reader accounts that they use to subscribe to all of their junk blogs? And, if they do dutifully subscribe to their junk blogs, would that not make auto-termination of said Reader/Google accounts pretty simple.

Wouldn’t Google have to try pretty hard to screw up something like this?