> OSS is usually like charity, you do it because you can afford to and want to and don't expect anything back from it.

There are reputational rewards associated with open source[1]. However, if you're solely contributing to open source for those rewards, you're going to have a bad time. I would agree that there needs to be a high degree of intrinsic motivation.

[1]http://www.catb.org/esr/writings/homesteading/homesteading