YC is by no means the first incubator. There were hundreds in the late 90's in silicon valley. Lots of junk, and few that turned out big businesses. Some of those big businesses failed in the .com crash simply because the capital markets imploded (and others because their business had been over-valued).
Yes coincidence. I have no affiliation with YC. Okay so take the biggest consumer apps in the past 5 years- Instagram, Spotify, Pinterest, foursquare, tumblr. They all pass the smell test. I threw in FB, Youtube, Twitter (on the bubble of pre/post accelerator), and a few others...
But of course YC doesn't count. Even though it was the first incubator by a couple of years. So of course has had the first successes.
Coincidence perhaps?
Why is anyone upvoting this?