Such treatment can be used to influence, without any explicit trade agreement. Same reason a lot of institutions, and employees therein, are not allowed to accept or receive gifts above a certain, relatively small dollar amount, or any at all.

Even if nothing is promised or offered in return or for trade between either party, there still exists the unavoidable factor of influence. Not to mention the fact that htc can withhold these perks from those that run the sub, in order to influence in some way.

There's really no need to give mod/similar capabilities to any element of the company. They want "easier" communication, there's a "message the mods" button, and discussion is in a convenient format and function, inline within the site. Then, of course there are the thousand other ways in which communication can be held on the Internet between parties. Mod powers seem to be of no particular benefit, only added potential for something shady to happen more easily.

It creates a condition in which astroturfing is a much more practicable endeavor for the company, but no added benefit to the community that can't be achieved in a way that doesn't leave potential for abuse.