They have been doing this for a while. I am going for Marathon Weekend (tomorrow!) and lots of the people on the RunDisney board reported this. They called me to switch, but I didn't take them up on it. I do like Skyliner. I even asked if it was available for any other resorts (like CBR or PO-FQ) and they said no. I asked them why they were doing it and got an expected "Disney magic" kind of response.
I will say that during my fervent, daily checking for AP discounts, the only resort that always had availability no matter when I looked was POR. Seems like this was being done to spread the guest load.
Turns out, wouldn't have mattered. A friend offered me space in an OKW 2BR, so I canceled all but one night of my reservation.