You seem to be basing your rejection of "gift economy" as a label for the latter on the basis that it's not done for entirely altruistic purpose. But that is generally true of gift economies - most people who participate in them (and I'm not just talking of software here!) are not doing it out of purely altruistic motives, and actually expect to receive benefit from such an economy as well. Usually this is cultural, but some people, like you, might consciously believe that it's the most efficient way to distribute goods (whatever their definition of "efficient" might be).

> I release my code under the GPL for selfish reasons: I want others to be able to improve it, and me to be able to take advantage of their improvements.

I suppose that metphor depends on what you think of community efforts. Like say, sharing a food recipe or a workout routine. I see see the framing as "giving it away". Even if your endgoal is an ultimately selfish search of "better recipe/routine to use".