As you are most likely aware, XNA is a .Net wrapper around the C++ based directX bindings. .. so my thinking is that if XNA is not updated when they remove the old math library (and MSFT just said they would not), that effectively kills it, or worse, math just got a lot harder to figure out for game development for the noobs. Am I communicating clearly? If not, I apologize.
Math library? XNA has its own math library supplied as a managed library. It doesn't wrap any of the old D3DX math stuff, if that's what you're thinking.
Besides, there's a LOT more to XNA than just a DX wrapper.