I don't get this steamworks shit either. Valve would never be as successful without Counter-Strike and the mod community, who brought exposure to an already outdated engine at the time. And now they give minimum to no support at all to the community... maybe some marketing "genius" thought they don't need to rely on their community anymore, which is of course a big mistake.
Distributing 3rd party mods on steam would bring the community together and reward the hard work we have put into these mods. But that also gets into legal problems, as they would indirectly make money with games that should be free (it would significantly increase half-life's sale in my opinion).