Oh wow. Media Play. That takes me back. I haven't thought about them in years. They were the source of a lot of my D&D purchases as moving to a city with Media Play in it coincided with me getting my first actual job after college...
(From
@darjr's update)
Some suspense for the weekend - does this suggest that we're going to find out that the Planescape core sold in the same numbers as the other three boxed sets listed there? I actually wouldn't have lumped Planescape in with those settings, because my perception was that it was a much more popular setting than the others...