Thanks for the reply guys, sorry for not getting this.

I understand how MMIO works, my point is that the graphics card has no dedicated memory and is using shared video memory, which means it's using a portion of system memory as it's frame buffer.

That's why I didn't think the graphics card memory ranges would show to be on the PCI bus but I guess it's just because the graphics card is a PCI device so it just shows them to be on that bus.