The stories I've seen on it (like in the Wall Street Journal) indicate that Disney is trying to get some revenue from folks who visit sites like this one. They see a huge market in people who enjoy Disney, and that market is currently being served by people who visit free sites to swap information, rumors, and general chitchat. They apparently believe that there is a large group of those people willing to pay $80/year for a membership at an "official" website where they can do the exact same thing.
I think they overestimate the market. Sure, some will pay, but most will stay on the free boards that are unaffiliated with Disney.