Haddock, By putting the IOMMU/GART in the CPU, AMD made sure of that.
While you're at it, why not argue for AMD adding PCI to the CPU? After all, you never know when some "lazy chipset architect" forgets to support 64-bit address mode in PCI.
I think you're reaching very far to find reasons why AMD would stick the GART on the CPU. Personally, I think the info is bogus, and the GART is indeed on the AGP tunnel.
Tenchu