XNA is a growing group of software tools that allow developers to more rapidly develop their games. Additionally, Microsoft wants to share tools and technology between its different platforms (e.g. Win32, Xbox, future platforms).
Vanguard is one of the chief early adopters of this ever-growing group of software. For example, we will be using technologies from Xbox live, voice communication, and already have the ability to play the game via an Xbox-style controller with a tiny keyboard attached to it (a TID).
There will be more information about all of this later.
Source: Official FAQ