Even though XNA is technically a platform for both PC and Xbox 360 support, it should be noted that the Wii remote support is only for the PC, care of the .NET framework, and those looking to truly bastardize the console wars by using Nintendo input with Microsoft's consoles can only shrug their shoulders, snap their fingers and go, "Aw, shucks." However, it now looks like homebrew enthusiasts can create games using the Wii remote while pushing PC hardware so far that the software couldn't possibly be played on the Wii itself.
Update: As noted by Brian Peek of Coding4Fun, the Wii remote support is actually a facet of the .NET library (not inherent, but you can download the library made by Peek or others). And since XNA supports .NET, so too does it support the Wii remote. Here are some examples of applications made using Peek's Wii remote library. Peek also pointed to a post by Hower discussing the Wii remote and XNA. Thanks for the information, Brian!