(moved to the suggestions forum)
Parity calculations, implemented at the operating system level, are why RAID 5 arrays built through the Disk Management tools in windows are so slow. For adequate performance, Windows Home Server would require a hardware RAID solution, and that would add significantly to the bottom line. So no, I doubt that you will see parity rather than mirroring.
However, if you feel strongly about this, you might wnat to submit a product suggestion on
Connect.