I guess that's true, when you consider something like patio11 and his BCC. It doesn't sound like he was pouring 60+ hours a week into that (or maybe he was, somebody correct me if I'm wrong, please).
But I'm also guessing that the set of startups that you can build with that small a time investment, is pretty small. Especially if you're talking about something that's intended to be a scalable startup, something that can be a billion dollar business someday.