I do not understand why the parent gets downvoted so much. I think FB can do pretty much what they please. If Apple is concerned for any reason, Facebook can simply ask them: "Do you want the Facebook Apps in the App store or not?" I think the answer will be: Yes.
By that standard, Amazon should be able to do pretty much what they please too, but we know they can't (see: in-app Kindle store / link to web store, etc.).
