Well, I recommend you see the video because what it does extends well beyond airplay-like functionality. SmartGlass devices can be a controller for games or a "second screen" for games - similar to what the Wii U will do. Sure, a Windows tablet can do the same sort of "Airplay" stuff that iOS devices do between the SmartGlass device and a Xbox, but that isn't what the thrust of the demonstrations were about.
One example was watching Game of Thrones on HBO Go, and their tablet was showing a map of Westros and the tablet was zooming into where the current scene was taking place (so you get a sense of where the different armies are). In other words, you get interactive metadata about the show you are watching. Another example was a football game where you could design your custom play on the touch device like a coach does on a chalkboard.
That is quite a bit of integration between the Xbox and the SmartGlass devices (of which Windows tablets can be one).