Yes, there are only a select number of rooms at each resort available for the
free dining.
I have read on some of the other threads that POR and POFQ have been excluded in some of the the past discount periods due to the bookings already being at a level that Disney has been happy with prior to the promo's coming out. Disney offers the promo's to fill resorts so if there are resorts that are already booking without the promo, there is no need for Disney to include them in the promo, same goes for dates.
If you are thinking about moving to a different resort to save that kind of money (I sure would

) then you may want to have a second resort in mind just in case POR is excluded or full. Good luck!!!