I was told by a Disney rep they wanted to phase out the free dinning, but with the economy it works as a big draw from families. They make up the extra in selling other things.
The dates are similar, but they release them based of the pre-book rooms and use it to fill vacant areas in booking.
Here is a list I started a while ago:

8/15/10-10/2/10package deal (
free dining) Visa cardholders4/29/10, exp 8/14/10
8/28/11-9/24/11package deal (free dining) Visa cardholders4/28/11, exp 8/27/11
8/25/12-9/29/12package deal (free dining) Visa cardholders3/1/12, exp 9/18/12
9/30/12-12/13/12package deal (free dining) Visa cardholders7/9/12, exp 9/29/12
9/2/13-9/25/13package deal (free dining) Visa cardholders5/6/13, exp 7/31/13

8/15/10-10/2/10package deal (free dining) for general public5/3/10, exp 8/14/10
5/27/11-6/2/11package deal (free dining) for general public8/16/10, exp 12/20/10
8/19/11-9/29/11package deal (free dining) for general public8/16/10, exp 12/20/10
10/2/11-12/17/11package deal (free dining) for general public8/3/11, exp 10/29/11
8/28/11-9/24/11package deal (free dining) for general public 5/2/11, exp 8/27/11
10/1/11-12/15/11package deal (free dining) for general reissued 8/24/11, exp 10/29/11
1/8/12-3/31/12package deal (free dining) for general 8/3/11, exp 10/29/11
1/8/12-3/29/12 package deal (free dining) for general extended 10/27/11, exp 12/17/11
1/8/12-3/29/12package deal (free dining) for general reissued 8/24/11, exp
10/29/11
8/25/12-9/29/12package deal (free dining) for general public 3/5/12, exp 5/18/12
9/30/12-12/13/12package deal (free dining) for general 7/12/12, exp 9/29/12 CODE F8Z
When staying at a Value Resort, enjoy the Disney Quick-Service Dining Plan, which includes meals and snacks at over 50 select Walt Disney World® quick service restaurants.
CODE D85 When staying at a Moderate, Deluxe or Deluxe Villa Resort, enjoy the
Disney Dining Plan, which includes meals and snacks at over 100 select Walt Disney World® restaurants. Walt Disney World® Theme Park tickets Enjoy admission to one Theme Park per day, each day of your ticket.
Valid for arrivals most nights:
September 30, 2012 October 4, 2012
October 19, 2012 November 1, 2012
November 9, 2012 November 15, 2012
November 23, 2012 November 29, 2012
December 10, 2012 December 13, 2012
MUST BUY 2 DAY PARK TICKET
T53 code to upgrade to deluxe dinning and pay difference at value resort
Y83 code to upgrade to deluxe dinning and pay difference at moderate resort
2013 Book through July 31, 2013 with your Disney's Visa® Card and Code HAB for Value Resorts and code KAH for Moderates, Deluxe and Deluxe Villa Resorts. 9/2/13-9/25/13 package deal (free dining) for general public 5/9/13, exp 7/31/13 Free Dining is being offered to guests ARRIVING during the following dates. A minimum stay of 3 nights is require
September 29 October 2, 2013
October 18 November 2, 2013
November 11 23, 2013
December 12 22, 2013
If you stay at a Value Resort, youll receive the Quick Service Dining plan for FREE. If you reserve a Moderate, Deluxe, or Deluxe Villa Resort, you will receive the standard Dining plan for FREE. (You can upgrade to the deluxe dining plan by paying the difference in cost per night).
NOTE: Ft. Wilderness campsites and 3-bedroom villas, Villas at Grand Floridian, Art of Animation Resort, Port Orleans French Quarter Resort, and All-Star Movies Resort are not included in this offer.
HAVE TO BUY 2 DAY TICKET