Agree people are always talking about it. But they're rarely doing a decent job of defining the culture, adhering to it, and hiring to it.
I'd actually take an approach of formally defining the culture once it has established itself (and is working well).
But well, there's still too many variables to consider. Personal culture of the founder(s) would be very important in picking the right approach. Although many people would like it to be,I don't see management becoming a hard science anytime soon.
And I totally agree that the founders drive and define the culture. It's their responsibility to establish it, manage it, and change it, if need be.