John:
There's no doubt that the PGA is trying to "upgrade" the quality of the layouts used in their championships. Personally, I think it has to do with their use of Valhalla for the 2000 PGA. Their reputation suffered tremendously when they used a newer, non-historic venue for the very important tournament. Of course, most any venue would have suffered in comparison to Augusta, Pebble Beach and the Old Course, but using a very young site (and which they owned) caused a considerable amount of bad press. So I think they are trying to make amends for this slip-up by going to some of the more historic courses such as Oak Hill and Medinah, etc.