If I made a map with the Quake 2 textures, put them up on a public server and let everyone download it and play it, that'd be fine, but if I went straight to releasing a map on these forums including the textures, which everyone would get off the server anyway, that's a no-no?
That's like telling me at a Japanese ramen noodle shop that I can't order a bowl of noodles, but if I went to the store and bought the ingredients for it, they could make me one. That makes absolutely no sense.