From a content creator standpoint, I believe Facebook is trying to "sprawl" into media-type endeavors and hosting. As in they'd rather have the super-cool-viral-video in their ecosystem instead of linking out to YouTube. This creates a lot of friction - the notion of enforcement at the potential cost of market growth. I agree it's a good thing they're doing this.
My guess is turf grab followed by backfilling features needed (demanded) by a mature ecosystem.
Started playing with Graph API. I was pleasantly surprised that it had matured with some user privacy preserving kabuki. Like issuing unique user ids per app. An earnest effort to make it harder to aggregate and correlate ids across apps. (Alas, deanonymization is pretty easy.)