Woah. This is actually a hell of a loop hole.

Think about it:

It takes hours for some people to download a mod on very slow connections. Some people pay to be premium members of public servers in order to get "bumped up" in line. Are they then selling the modification?

Therefore, someone could, hypothetically, sell the method by which it is distributed: namely via CD. As long as he does not sell RTW itself, this could be legal. After all, the modifications require the software from RTW to function. Again, he is not selling the intellectual property. He is only selling the method of its distribution. By the same token, somebody could host a super-fast server, bittorrent style, and sell the service, but only exclusively for downloading mods.

Woah.

If somebody decides to really run with this, they would likely end in court either way. Its just hard to say who would win, because the law gets fuzzy when dealing with the distribution of free software.