This is exactly my point. Will he quit the paying job to work for free? How long could he maintain this for free with no other job, or with a job and additional free hours without running out of money or burning out?
But everyone can't realistically live a wealthy life off FLOSS tools either. The people who write these things are usually very talented and will make killer pay anywhere they work. Usually a cool thing is when companies sponsor them to work X% for them and Y% on the FLOSS tool.