The Apple TV, for all intents and purposes, sounds as if it is an iPod that you put on your home network and connect to your TV. It shows up in the “Devices” list in iTunes.
The Apple TV is based on Mac OS X; that’s how people have done some hacking on it.
So why don’t the iPhone and iPod Touch — software for which is also derived from Mac OS X — have network-based synchronization? Are they merely one flashy keynote address away from having it? And why not have introduced it before the new Zunes came along with that feature?
(Of course, you could ask the same question about other technologies, including Bluetooth A2DP.)