I don't care for your DRM argument, the only place were DRM is annoying is in singleplayer games. (Or in online games that are not Beta for that matter, which is again discussable because mmorpg's generally also have DRM)
The devs can do with their mod as they please, because they are the ones who are developing it.
EDIT: The reasoning I see here is that a modification should not have DRM and should enable private servers because it's a free mod.
- The fact is that the mod is still in Beta and the devs want it to be released in a "controlled" enviroment and to be honest I have nothing against that, almost every game that has an open beta stage, also has a controlled enviroment where no private servers are allowed. So why shouldn't (or can't) mods have that as well?
- The modification will allways be the intellectual property of the devs, so they can do what they want with it in my opinion.