No one really says they have to. As Jobs said it won't be the only way to get Apps. But smaller devs benefit greatly. You can go from 0 to collecting payment

No one really says they have to. As Jobs said it won't be the only way to get Apps. But smaller devs benefit greatly. You can go from 0 to collecting payments worldwide, having distribution, updates, a 'store' to display your product, etc. with very little work (in comparison to doing it all yourself).