I'm not sure. Correct me if I'm wrong, but recall that the standard for x86 machines isn't the x86 itself, it's the fact that they're all technically derived from the standard architecture of the 1981 IBM PC. PPC architecture never really had a standard reference model like that (at least, not with the dissemination and manufacturer buy-in of the PC). As Piru says, Macs are the closest thing.
Common Hardware Reference Platform CHRP was an attempt until........Jobs came back.
