[rawr]

>> "When programmers develop 'for fun' we write documentation."

That's because they get something out of it. Namely, people won't use undocumented software and the authors want their software to be used.

In a corporate situation we don't document our software if we don't have to because we don't care (usually) whether or not people use it. If the company cares, it will force engineers to write documentation and we will do it because we don't want to get fired.