[sp332]

Actually, most kernel hackers (and I'll extrapolate wildly and say most open source programmers!) are paid to hack. PDF, relevant bits are in Tables 6, 9, 10, and 12. http://www.linuxfoundation.org/sites/main/files/publications...

[Charuru]

If you're talking about os products that are supported by a company, there are a great deal of paid designers, eg mozilla, webkit, android, etc.

Just in this context of getting people to 'contribute', we're explicitly referring to projects where the developers do not get paid.