I always wonder if the people who spend so many hours writing code for scripts like phpbb do it just for fun or if they are somehow getting some sort of monetary return. I'd be interested to know how some of these open source projects make money if they do.
Most projects are hobby and/or fun. Some open source developers, such as the programmers at Redhat, are paid a salary to code open source projects, same with Open Office from Sun, and other such big name vendors. I've talked to some developers of phpBB and none that I know of have received any sort of compensation. We all know phpbb.com sells text links, but I imagine most of that money goes to hosting.
It could also be a form of 'selfishness'. As an example, where I work we use the Mantis bug tracking system (and have done for years). As our usage got more 'unique', our code became more different: it got to the point where, after merging all of our in-house changes, the diff file was half the size of the original codebase and it was taking around 3 or 4 weeks to merge to the next version. In my case, the most 'selfish' thing to do was make our code more generic and then get it merged in to the main code branch. That way, the next version had our changes and voila, no more month long merging. At the same time we were able to give back a large number of changes and so help the project out. Win-win, which is essentially what FOSS is all about.