A lot of art seems to be produced even though winning or loosing is involved. Just check out music competitions or drawing contests.

Games can be a rich expression and some of the results are certainly art.

Khronos, the main authority of OpenGL ES, tells that it "consists of well-defined subsets of desktop OpenGL"

http://www.khronos.org/opengles/

GPL is not just incompatible with iPhone. (L)GPL is also incompatible with proprietary development environments on game consoles such as PlayStation 3, Wii etc (except for PS3 Linux obviously).

Just use the Zlib license and feel flattered if people consider using your software. Even if they don't give credit. Even if they don't contribute back.
Some will contribute back or give credit voluntary, even through they are not required by the license.

You can publish your source code, just avoid re-distributing proprietary technology.