Like Many said. If Apple were to make a special chipset then it would properly be a single chipset.
There would be no Floppy port, no parallel port, no IDE Port, no Serial Port, or PCI lane.
Simply just PCI- Express , SATA, USB, Firewire, FSB.
It would be legacy free, but it wouldn't save much cost. Since the die area used by those are pretty small.
It would use less pin, i guess they could have less PCI Express lane then industry standard. So they save cost with less...