Not all open source need be GNU though.
Consider that a BSD style license allows un4seen to maintain its control over the project and its "official direction" without a hundred-thousand Xmplay's running around vying for community popularity. Most developers around such a license submit patches (after screening them with their developing peers) for hopeful inclusion by those with oversight over the project.
One of the bad parts is preventing the stock ticker, the built-in webbrowser, the e-mail client, and the global positioning system from getting stuck into XMPlay, and just trying to keep it as "just a music player."
I'll admit when I saw xmplay the first thing I went for was the source code and was disappointed not to find it, but I understand its reasons (I had wanted to change one little thing that was bothering me for personal use only). I know there are projects out there like OpenCubic and the stuff Jeff did for Impulsetracker to provide the formatting structs and specs and whatever else to design a player engine of our own. I don't know if anyone has ever comprehensively archived them all but it wouldn't surprise me if it could all be found on one website out there.
As a poor solo programmer trying to cut out a living in a world of outsourcing and brutal corporations beating their labor to death, I'm a bit slow to critisize people for not going to open source, but in a spirit I try to make my programs very customizable for the end-user if they want to go technical (I notice XMPlay also does this, as well as Firefox, NWN, and countless others). Closed and Open are both good things, just for different reasons. Sometimes Open products are better than Closed, and sometimes the other way around. A lot of the time it just comes down to who is maintaining it, or if a company has good people or not versus the project's people.
There is also a certain amount of question of how much Closed copies material from Open, and Open developers with Closed source jobs taking company IP and putting it into their Open projects. Usually it doesn't come down to blatant copying -- the algorithms vary for individual needs. I don't think its talked about much, but it probably happens a lot. Really both complement eachother.
