Just because Microsoft supports it doesnt mean your Windows box will start scanning your files for copyrighted matireal. Microsoft supports alot of things and not all are parts of Windows. For example Microsoft officially supports HD-DVD but that doesnt mean BluRay is locked out of Windows.

Even if this somehow did manage to make its way into the OS, I dont see how it would be effective unless Microsoft's lawyers to developers ratio was 100:1 and the company changes from a software company to being the Cloud Police (or Series-of-Tubes Police, whichever you prefer). That aside, technologically its pretty hard to distingush what on my local FS is legal and what isnt (not that I've ever pirated any movies or music...) because by law I can make backups of everything I have and its hard to distingush something a user downloads from BitTorrent from some video they made at their kids birthday party, its not like every video you grab off the Torrent networks comes with a meta description "THIS VIDEO IS PIRATED! CALL THE MPAA!"

My $0.02