OK so now I have tested the ETQW demo without libtxc_dxtn.so (i.e. without S3TC) and it even cannot load the level (it looks like textures seem to be the problem). Game developers don't care about Mesa, I bet they have *NOT* tested the game with S3TC disabled. Who would expect a driver to not support S3TC nowadays anyway?
So I have to consider r300g to be ETQW-ready no matter what the article says. Gonna kill some marines with my Lacerator, see ya!