Airplay ad-hoc WiFi?

I've been looking into getting some wireless speakers for my iOS devices.

AirPlay seems to be the new hotness. But is it true that both speakers and the device need to be on the same WiFi network? Does Airplay support ad-hoc WiFi? It would be nice if visiting friends could use the speakers without having to give them my WiFi password.

On the other hand, anyone can pair to a Bluetooth speaker.

What's the advantage of Airplay speakers over Bluetooth speakers?