[psook]

The implicit fault in the OP is that the developers don't get anything out of providing support. This is entirely false, however, as your users are your testers. If the product isn't good enough to pay for, as many projects are when they start, or fills too small of a niche to justify a payment from someone, you risk your project becoming stagnant due to no user-input. When others use open source projects, their specific goals for using the project might vary slightly from the developer's, and the use-case will never be fleshed out--leaving the project at a lower quality than it could be, limiting appeal and growth.

That doesn't mean it's the wrong choice all the time, but these are the tradeoffs that you're making when you make that choice.