Dryspace: I certainly wouldn't say 'never'. That is exactly what I might be liable to do--and recommend that others do--if I have no reputation, and believed in a product and personally thought it would be successful. Again, it's a choice made on a case-by-case basis.
I wouldn't condone it personally, is perhaps a better choice of what I should have went with. Signing over the rights to something you created in hopes that what your creation is in might prove to be an overnight (generalized) success that would in turn bring you more work is just something that seems far too risky. Likewise, you could also be signing away rights to something that could potentially never end up finished (for any number of reasons) and if you didn't work out an agreement that if such a product is never finished to allow you to use/distribute the music (or art or similar) in some form, you're left with nothing at all.
Dryspace: The thing is, it's not necessarily the musician's "work". It's only his if he owns the attendant rights. What a musician does with his mind and body are not sacred and fundamentally different than what an architect or waiter does with his.
But my point is that if I were developing, say, The Legend of Zelda, I may well want to secure the rights to music so that it is only heard within my game and remains unique in that way. It is my right to ask that of a musician, and it is a musician's right to accede to or deny my request.
I think I understood where you were going with that (I'm not going to pretend I have a complete grasp on everything, but I'd like to believe I'm scraping by).
I think you may have misinterpreted me though - in that I didn't mean "if you write/perform that music, you and you alone own the rights", more that any composer should be working out with a developer that they both have the freedom associated with their respective creations: namely, as you put it, a developer being free to continue marketing their game with the music provided in it but at the same time, the developer acknowledging that said music is the property of the composer and the composer can (if they decide to do so) sell it outside of the game. The situation becomes a mutual win/win for any involved parties.
Also, and this is my own fault for conveying it badly, but I'm not extending this argument to a broad sweep of every person's contributions in any field (to go off your example - I don't believe an architect could then lay claim to a building they designed solely because "it was their design" nor do I believe any artist selling a painting could then drop into a buyer's home and reclaim it because "they painted it").