It was in April this past year. You have to request the free dining during the announced period--they don't automatically give it to you, so make sure you call early, so you get your first choice of resorts--some booked up this last year!
It doesn't work that way. There's no pre-determined list of resorts that offer free DDP and resorts that don't.
When free dining is offered, it's not offered across the board for every room in every category in every resort. Free dining is an incentive to get more people to rent rooms. If enough rooms in a particular category in a particluar resort are already sold, then Disney has no need to offer people an incentive to rent more rooms.
So if Grand Floridian, for example, is nearly sold out, Disney doesn't feel it necessary to give something away for free to rent out the very few remaining rooms. They obviously don't have to give away something for free to attract customers if they already have just about sold out the joint. Know what I mean?
Another thing to be careful about when looking at Deluxes and Free Dining is that it has been that you have had to pay "rack" rate (no discounts) on your room portion to get Free Dining, and since the Deluxe rack rate can be pretty high you had to be sure and calculate that you were actually getting the best deal. There was a separate package special offer that came out last year for the same dates as Free Dining and I remember some DISers posting that they had a better deal at a Deluxe using that deal and just adding dining, so be sure and price it both ways...all depends on number of people, etc. Of course we don't know that it will be the same this year though!
Values were a no-brainer and were always a great deal, especially with kids along!