With all due respect (and I'm wrong a lot!) Google left quite a bit on the table. Their stock price went up 500% from $85 over the next year. Wouldn't they have been better off capturing some of that?

The jury is still out on Facebook. Their IPO could hurt them getting money in the future, but maybe not.

It's not the underwriters who get paid when stocks double, it is the people they allocate the stock to.