[webwright]

"Maybe PG just expects these startups to build a quick product and sell off to a Google, Facebook, Zynga etc."

YC makes very little on quick-flip startups.

Count the number of YC partners and the number of LPs they have, do some napkin math on their expenses (weekly dinners for 150+, funding 120 startups per year, presumably moderate salaries for partners and staff, legal bills, flying hundreds of people to SV for interviews every 6 months, etc), and tell me how needle-moving it is for them to turn a $20k investment into $240k (before taxes)... Which is exactly what they'd get for a $4M exit.

AFAIK, YC always advises founders who have an early flip opportunity to stick it out (though it's supportive if the founders don't want to do so).