Good question as that policy is clearly stated. Here's your answer.
WhyPark, as the name denotes, is not a traditional domain parking service. I know I've used the term "parking" quite a bit but WhyPark is really a content hosting service.
Traditional domain parking services display no content on the parked domain page. They add no real value to the web and that's why Google will not allow their ads to be displayed on them.
WhyPark allows you to create an unlimited number of custom pages and load them directly to your hosted domain. They're really just mini content sites that you can customize. Not just a blank page lying out there with Adsense ads plastered all over it.
For those of you with a BUNCH of domains, probably in the 1000K+ realm, Google themselve's offer a pretty much unadvertised Domain Parking service which you can review here:
http://www.google.com/domainpark/
Funny part is their domain parking service displays ABSOLUTELY NO real content. It just dispays their ads...hmm....what's good for the goose is good for the gander is it not? I may investigate this service further to see what the requirements are.