Honestly? I really don't see the problem - provided that they don't just start charging for what's already there. If you can play online for free, and they just add a "premium" subscription on top for extra skins/automatic and constantly updated DLC, is that really a problem? Are you all really so cheap as to think that a team of developers spending their time creating new content should give it all away for free? No, because they need to pay those salaries so the people who make the stuff can actually feed their families.
The whole "DLC should be free!!!!1" argument has always sounded so juvenile and immature to me. If a team of twenty people works for a month to create something new, in what world should they NOT get paid for their efforts? Similarly, if Treyarch starts working after the launch of Black Ops to release a steady stream of new content for their game, should they not get paid for it? Is their time literally worth nothing?
And I have to say, if you think Valve constantly updates TF2 out of the pure goodness of Gabe Newell's heart, I have a few bridges to sell you out in San Francisco. That's as much a business decision as anything Activision does. It keeps you on Steam, it keeps you seeing their ads and buying new games on Steam... and Valve gets a cut of every game you buy. It's a loss-leader.