MS would do a lot better to buy 200 promising startups (especially in the mobile space)
b) Individually, not terribly likely. Collectively? Sure. (And it's $35M each, but the exact number isn't the point - let's say you could offer every ycombinator and techstars startup an average of $35M each, you'd likely end up getting two or three Dropbox-esque gamechangers, a few dozen decent products, and 150 otherwise good ideas folded into MS and dead-ended.)