There are about 5 questions that feed into "who is going to pay you?" All of them are pain points for the vast majority of startups (anecdata). Idea + development + customers = Business. I'm not saying PG is a dope or anything, but it has to be apparent that the "customer" chunk is an Achilles heel for just about all dotcom-y biz. The ones who aren't getting funded for being gadget new tech, who aren't going to be bought as a team for implementing a possibly-useful technology, are going to have to figure out who the customer is, and from reading HN it seems most are counting on the first two options.
