It means, there is no source code and no radiant (radiant = the map editor) attached to the game (you dont need that to run the game).
Very true - If you really had a legit need for the source code (and the programming skill to do anything with it) you would be better off getting it from SVN instead of one of these downloads, and yes, as Ain Soph Aur stated, you don't need that to run the game.
As for the map editor, since it is a much smaller packaged size I can upload installers for just that more often.
@Muton: Hey, you really seem to know your stuff when it comes to programming, have you thought about becoming one of the project coders? Even if you wouldn't commit code on a regular basis, even a little once in a while, I'm sure we could use you.