No, I’d say the App Store,

I consider it a device perk. I bought the iPhone and Apple TV largely because of airplay so if they remove that functionality it will move me to use other streaming services that support it or I’ll just buy movies again and stop paying streaming altogether.

Required by store?

This is such a good answer, it puts the entire situation into perspective. About who wants to (and theoretically should) act in favor of consumers.

Its a selling point for Apple and Google devices.

Buy into their ecosystem and things "just work". Except when they don't.

Its a cross cutting requirement that adds value for the platform.