Sure, but the rules are completely arbitrary. What if they suddenly say only apps distributed in the MAS can use AirDrop, CoreData, CoreAnimation, etc.? It's

Sure, but the rules are completely arbitrary. What if they suddenly say only apps distributed in the MAS can use AirDrop, CoreData, CoreAnimation, etc.? It's not as if they will bother telling developers beforehand. Go look at the Apple developer forums today, under the iOS 7 beta section, people only found out that the iOS App Store allows older versions of apps to be downloaded because 9To5Mac found out about it and published a blog post. No official guidance (as yet) has been given to developers.