If you look at Apple's Mac Pro page, it claims that the Mac Pro is "Quad Core". And remember the Power Mac G5 "Quad"?
This is just marketing. While I agree that it is dubious of Apple to use these terms interchangeably and muddy the waters like that, in this case, Apple is talking about the total numbers of cores in the system rather than the cores per chip.
EDIT: I see that they explicitly say "quad core processors" in the ad. I still think that is a marketing slip-up rather than anything else, due to Apple's heavy use of the "Quad Core" term in other references to their pro desktop products.
This is just marketing. While I agree that it is dubious of Apple to use these terms interchangeably and muddy the waters like that, in this case, Apple is talking about the total numbers of cores in the system rather than the cores per chip.
EDIT: I see that they explicitly say "quad core processors" in the ad. I still think that is a marketing slip-up rather than anything else, due to Apple's heavy use of the "Quad Core" term in other references to their pro desktop products.