> Well, OK, it's 2 PPC cores, but it's also PCIe.

Apparently, reukiodo's nitpicking (and my counter-nitpicking) made you confused :-) To explain it: With "G5" you meant the PowerMac G5, to which reukiodo essentially replied that "G5" was the moniker of the processor chip, of which there're 2 in said machine (to which I replied that in this case, there was no PCIe in the "G5"). So in summary:

G5 machine (2.5 GHz PowerMac11,2): 4 PPC cores, PCIe
G5 processor chip (PPC970MP): 2 PPC cores, no PCIe

The PCIe on the machine is provided in part by the IBM CPC945 northbridge chip ("U4" in Apple speak) and in part by the ServerWorks HT-2000 (aka Broadcom BCM5780) chip.
I hope it's as clear as mud now ;-)