For what it's worth, there is plenty of availability on expedia for those dates. It's all at rack rates, but all the biggies are there. BWI ($289), Beach ($289), Poly ($299 garden, $385 lagoon), GF ($339/$400), AKL Savannah ($275), etc. Even for resorts where Expedia is showing that not all days are available for the three resorts, it seems to have availability on the Saturday and Sunday. Interestingly, the Friday seems to be the day when most is sold out.
Expedia room availability is frequently different from Disney room availability, because expedia has its own inventory. But it's usually a very good proxy for figuing out how much demand there is going to be and whether stuff might open up. Expedia only takes an option on the rooms, so if they don't sell them, the rooms go back to disney. At a minimum, lots of inventory comes back from the 10 to 5 day prior to check in point, due to the fact that people wait until the last minute to cancel. (If you want to play around some time, go to wdw web site and check some dates, and then 5-7 days before those dates check again; you'll be amazed what pops back up even in busy times.)
Also, someone posted here once that when disney says a resot is "sold out," it doesn't always mean all the rooms are full. In low demand times, they don't always make certain halls or wings available until they have measured that demand will justify it. (I don't really understand all this; it would be great if someone who does could explain it better than I just did.)
Finally, even if the rooms were sold out, we've been to WDW a few times when there was seemingly low supply of rooms but the parks were near empty.