My Thoughts on MS Tablet Strategies
MS Surface is for both media consumption and media creation, while Xbox Surface is mainly for media consumption especially games. Xbox surface will be the hub for Xbox music, Xbox video, games and maybe Xbox books (I think they will launch the service sooner or later).
Xbox surface may be bundled with the new Xbox 720 as additional controller or serve as Smart Glass. Most probably it will be able to install Windows Store Apps even though it uses different Windows Cores.
Just my wild speculation. :D