Clearly, they've decided that getting people to pre-pay---and thus commit---to Disney vacations long-term is in their best interests. Because DVCers feel like they've already paid to stay there, they're much more likely to come even in down times. True, some might just come and hang out in their resort, cook meals, and swim in the pools, but even in tough economic times, I don't think the fraction doing that will be large.
And if that number is significant, Disney can cope via reduced hours in the parks, reduced events (i.e. Fantasmic isn't running nightly), reduced restaurant hours and staffing, etc. They know very well how to make certain attractions "seasonal," how to run a parade only three times a week, how to remove and add characters from a meal, and only take reservations for a half full restaurant because you don't want to have a full staff.