This has less to do with Apple vs. MS as it does ATI vs NVidia and Intel vs AMD.
Every new pc will be able to be a HD 720p tv/pvr in a matter of 4 years.
I don't think Apple will be able to maintain first to market because of their small user base.
All I need for turning this pc I'm writing this on into a 720p hdtv/pvr is for my cablecompany to remove signal blocking, or buy a ~$1500 piece of hardware from Norway, Austria or Japan to shift the signal.
You can already turn any old PC into a PVR and I would assume(I maybe wrong) that a HGDTV convertor/ready TV would take care of the HDTV issue.