The problem with his reasoning is that the big banks are evidently quite safe. No matter how bad their investments are, the government will bail them out with taxpayer's money to prevent them from collapsing. I doubt the same would apply to a bank ran out of somebody's basement.
"People are dramatically more productive as founders or early employees of startups—imagine how much less Larry and Sergey would have achieved if they'd gone to work for a big company—and that scale of improvement can change social customs."
I question this assertion. I'd bet a single Google engineer who makes a 1% improvement in adsense targeting can create more economic value than most startup founders.