Why Microsoft Won't Have Blu-ray on the Xbox
You are comparing apples to oranges. The windows OS is designed to allow third-party applications to run on it for a nominal additional cost (price of a dev kit) to the third party developer. The Xbox is not. Please, examine Microsoft's license terms carefully before you blindly assume the xbox is open.
More specifically, Why let consumers pay for their media once with a blue-ray player when Microsoft and the media distribution cartel can (and will) earn far more money passing it through the xbox?