Technically, you could always develop for Windows using OpenNI however you'd typically be relying on a 3rd party wrapper to expose the bindings in .NET. I'm not sure if this library is utilizing OpenNI or has been built from the ground up, but regardless: it does encourage developers to use their library rather than a separately maintained one.

In saying that: OpenNI works pretty well with the Kinect if you spend some time understanding it! I've never used the Windows bindings however on OSX it works well :)