... for a possible source of the differences seen by 32-bit and 64-bit processes, see the section entitled: "What is Not Virtualized?"

Yes, that seems to fit the bill quite nicely - thanks. Hard to believe that "Microsoft intends to remove this form of virtualization from future versions of the Windows operating system".

Btw, after looking at this bug report, I did find that opening HKEY_LOCAL_MACHINE for KEY_READ access only (with x64 perl), did allow me access to the key in which I was interested, without having to run as Administrator.

Cheers,
Rob