Apple Computer, Inc. -> Apple, Inc. -> Apple Gadgets, Inc.
You're forgetting that AirPlay is a whole house audio solution similar to Sonos - local hardware (Airport Express units) need to communicate with each other over the wifi network to get the audio in sync.
Perhaps Apple will release a cheap Airplay Dongle like Google did for their ecosystem. Though I won't hold my breath. #Apple.
-> Apple Dongles, Inc.