According to brent rector, Microsoft actually tested and ensures those WinRT APIs not related to Metro UI or app model, eg. Networking APIs, to work properly in Desktop apps.

http://channel9.msdn.com/Events/BUILD/BUILD2011/PLAT-876T

and during the Going Native Live at BUILD, the WinRT team are just focusing Metro scenarios in this release, and they are open to consider WinRT for Desktop apps after delivering this release first.