I think you're probably looking at the success of the FTP as well as many of the POFQ people getting upgrades to the deluxe resorts.
That's probably the reason so many of the other resorts were limited at times in October and November also.
I know that when I called about the FTP in April or May, the first thing the CM told me was that she was hearing that GF was already booked for a week or two in October.
Since the AP rates are generally offered as a portion of available inventory, there probably were not enough available rooms in September to make offering the rates worthwhile for Disney.
Of course, with all the people who keep saying they book a room and wait for the discount, they may have shot themselves in the foot, cuz if those rooms were not showing as booked, it might tip vacancies to a point where AP rates would be offered.