Silicon valley is a lot larger than just web start-ups. If and when YC launches something that eventually turns in to the next google or something on that scale it will have a real impact, but for now the big winners have not been created using the YC model. Who knows, maybe one day.
Google _was_ a web startup, and there's no reason that it couldn't have come out of yc. Also, a fair number of yc startups are not "web startups", whatever that means. (do you have to make hardware to not be a "web startup"?)