They're unique arrangement with Netflix predates their Video Partner Program and probably some of their other app store rules:

Peter Stern:

"Longer Version: I explained that these IAP tests are not OK for Apple. Our commitment to developers and customers is to run the world's best App Store, and when Netflix is cycling in and out, they are undermining that. I also explained that we run a principled App Store, and they have a unique arrangement because it was struck before the existing Video Partner Program came into effect..."