To be fair, AirDrop requires you to be on the same network as well, as otherwise the devices don't have any way of communicating. If you're already on the same WiFi, it'll use WiFi but if not, it'll connect to each other via Bluetooth (eg, connecting to the same network [a network of two devices]), but the setup of the connection is automatic.
Maybe Snapdrop can do something similar with the new Bluetooth Web APIs.
False. AirDrop does discovery via bluetooth, but then sets up an ad-hoc WiFi connection directly between devices to transmit data. No network required.
That Airdrop sets up its own temporary network hidden from view is not really relevant to most users though. For the user, it just works like "magic". All you need are two phones.
That was the initial version of AirDrop that had the same network requirement; future releases negotiated an adhoc wifi connection over bluetooth then used that.
Maybe Snapdrop can do something similar with the new Bluetooth Web APIs.