DRM Recordings Tied to PC or MAC?

Everyone notes that protected recordings under WMC are tied to the PC they are recorded on. But are they really tied to the PC or are they actually tied to the Ethernet MAC of the first network adapter? I know for most this is a distinction without a difference given the prevalence on on board Ethernet on motherboards these days. But if one could disable the on board Ethernet and use a PCIe based card instead, would the recordings be portable to that card?

It would be nice to be able to save recordings when upgrading an HTPC's system board by moving the card to the new unit with the drives if possible.

That's depressing. I assume a GUID is created at install time (using time + MAC) to be used as the DRM key then. Thanks for clearing that up for me.