I don't think that's quite right either, that they go to people who haven't been there in awhile. I truly believe it's random after our experiences.
We've been to WDW 14 times, 8 of those since March 2001, and we have our next trip booked for April. Last May we brought some extended family and friends with us, including my 6yo cousin. She got a postcard in the mail with a discount rate sometime last spring before we went, I think in April. It came to my house (res. was under my name and address) and I was shocked as I had never gotten one and then a 6yo does! We couldn't use it for our May trip because it didn't apply to the room we had booked so it went unused and I threw it out (since we would not be vacationing with that cousin ever again).
Then, a few months later, my mom (who sometimes comes with us), my husband, and I all got e-mail codes good though the end of 2004. My mom's came to one of my e-mail addresses, not her own. I think it was in July. Well we didn't plan on going back till April so we didn't do anything with them (in fact my husband deleted his). Then we got cheap airfare so we decided on a last minute December trip. I thought about the e-mails we had received and dug them out. My husband's was deleted so that left us with the 2 sent to my e-mail addresses. The 1st one came up as linked to my cousin (not the 6yo, a 23yo who also came with us in May) and the CM said I could not use it. The other one I got at my other e-mail address came up under my mom's name. That CM was going to let us use that one, but there were no rooms available with that code where we wanted to stay, so we booked with the
AAA rate. So both of those codes went unused also.
We went to my mom's house for Thanksgiving and my mom gave me a pile of 'junk' mail I had received there, including a postcard sent to my husband for a cheap rate at a moderate. We didn't try to use it for our December trip since we thought all codes were the same and if there were no rooms with the e-mail code then this postcard must be the same. We were probably wrong but we had been able to apply our AP rate so we didn't care, but again, the code went unused.
A couple of weeks ago (not sure of the date now), my husband got another e-mail with the code for this spring, which we used for our April reservation.
So including our trip this April, we've been to WDW 5 times since May 2004, and stayed at the GF twice, AKL, Pop, and ASMu and we'll be at AKL and CR this trip. So unless they want us to try out a moderate next time (that's what the postcard advertised, POR), I can't figure out why they sent us these codes.