Not that I'm a strictly a business guy (I straddle product manager and hacker roles), but there are quite a few things, depending on the product/service, that need doing that aren't directly related to building the product:

* The "idea" stuff, also known as product management- defining features, writing requirements, market analysis to make sure you're going to achieve product/market fit, etc. Developers can/should have a say in this, but it's not always a match for all developers' skillset.

* Bizdev - lining up distribution, partnerships, and customers-- talking to them to make sure their needs are being met in the product, and making sure there is sufficient revenue/incentive to keep everyone happy

* Keeping the books, writing the appropriate bizplans/marketing plans/etc if bringing on investors is on the horizon

* Engaging outside resources - legal, accounting, office, contract workers (designers, developers, whatever core competencies aren't on staff already)

* Project management/cat herding