Like Joel said, isn't there still some selection bias there? I would think that even the people you've met because of YC are the ones who are connected to the outside funding "world" in some way.

I don't see where. I've met them (a) because they come as investors to Demo Day, (b) because they're famous founders we've invited to speak at YC or Startup School, or (c) at events like conferences, Foo Camp, etc. Where would there be selection bias in any of those things?

Perhaps it's more of a negative selection bias.

I know 9 people who have made $5-$10M from software companies they have founded without taking outside investment. Most of the money was made by selling out to a bigger company, although one guy still is doing his thing.

They don't go to conferences, aren't famous and don't invest in startups. Maybe that amount doesn't count as being rich, though.