IIRC pg has somewhere said that it would be in YC's interest for their startups to become massively profitable (and IPO or whatever), instead of getting bought out early. That is, YC's slice of $20 million is a fantastic outcome for YC... but a slice of $200 million etc would be even better.
This led into a discussion that YC's policy is to just do what is in the startup's interest - if they want an exit, then YC will support that. And after slaving your guts out, pretty soon $20 million in the hand is starting to look pretty dang good! pg mentioned that instead of trying to calculate exactly what is in YC's interest, with so many startups going, the simplest approach is just to do what's in the startup's interest. I think everyone - including pg and future candidates - also feel a lot more comfortable with this approach.
But I have to say: $20 million! That's freakin awesome! It's presumptuous of me, but I feel really proud of you guys. Go go go! And thanks also for posting a figure; that's usually secret.