iDevices use a multipin connector, so they can do all sorts of things through it. Android devices use a specific arrangement in the earphone jack for a couple of functions, but the USB connector is basically 2 pins for power, 2 pins for data and, on some phones, video. You can't do things like switch tracks on the same wires the sound is coming out on, but they're the only wires the standard Android spec calls for. (Actually, it doesn't even call for sound on the USB connector.)