Have a feeling people are reading too much into that, too.
People (at least that one person I quoted who assumed way too much) see 'MMO' and their brain links immediately to MMO conventions as we know them now. What's far more likely is that Bungie have sprinkled MMO elements, such as persistence and how the world behaves on top of their new FPS formula to make some unique hybrid that can be loosely defined as massively multiplayer.
I doubt Destiny will have a subscription, and I doubt we'll see quests that ask the player to grind 10 'Fallen' pelts, or whatever.
Those seemingly perturbed at no PC announcement also need to understand just how much Bungie had to scale their studio to create Destiny. They already hired vast numbers of people to produce a Playstation 3 version, staffing up for PC development and the unique challenges that entails to match the standard that Bungie sets itself (in terms of community engagement) would've been an enormous task. Especially considering they're targeting next generation consoles as well.