...the PGA is hosted on courses that don't measure up to the sites of the other majors...
Balderdash. The PGA has locked up sites the US Open would like to use, so the US Open is off playing places like Torrey Pines.
Torrey Pines is absolutely unworthy, I'll grant you that, but the USGA has to go to California and it likes dealing with municipalities as opposed to private clubs whenever possible and that's why Torrey beat out Riviera, but you can't seriously argue that the PGA is regularly contested on better courses than the Open. Can you spell Valhalla?
Can you spell Congressional?
The US Open is going there again in 2011, and GD has it rated significantly lower than Valhalla.
My point was about the PGA collecting sites that the US Open used to use and has not returned to recently. E.g., Riviera, Medinah, Hazeltine, Oak Hill, and Baltusrol. It seems some of these prefer to deal with the PGA over the USGA now. Of course there is also the coup d'etat that the PGA has locked up and the USGA highly covets, Whistling Straits.