But I've spent years in both startup and non-profit contexts, and I think intrinsic motivation is much more powerful, especially for work that requires creativity. The best people I've worked with, even in startup contexts, weren't focused on the money. They liked making things and solving problems.
And I don't think it's just my experience. McConnell's Rapid Development has data from surveys of developers; they were much more motivated by things like responsibility and challenge than they were by cash.