This has always been my impression of how it works. Disney can't just take rooms from DVC and sell them for cash. Timeshares are regulated and members have an ownership stake in those rooms. Sure, theoretically Disney could just be lying and cheating the system, but I'm skeptical about that given how big and popular they are and how much public scrutiny and bad PR they would get if they got caught -- and with all the public discussion and information about Disney/DVC out there they would get caught sooner or later. They wouldn't be able to fly under the radar.
Anyhow, if people are using their points at other places that aren't their home resort or WDW (DCL, DLR, Aulani, other Disney hotels worldwide, RCI, Concierge collection, Adventures by Disney, etc.) then rooms that previously would be allotted to points/DVC get assigned to Disney for cash sales. I think the technical way it happens is that DVC "sells" the owned points room to Disney (I guess the hotel division) and then uses that money to "buy" the RCI reservation or the vacation package from Adventures by Disney.
If there are more "cash" rooms at DVC resorts than in the past, it likely just means that DVC members aren't using their points at WDW as much these days. Which wouldn't be a terribly surprising thing given that the park hasn't been adding much, so much like many people on this board are saying, people might be doing other vacations with their "money" (in this case DVC points). And a lot of those vacation options take up a lot of points -- a family of four that goes on a week long DCL trip could use 650 points or so easily which is like 2-3 weeks in a two bedroom villa at OKW/SSR.
