Only one true external display yes... for the MBP.

For the MacPro (tower machine), you can get up-to 12 displays with the right Video Cards... easily and be supported right away with little to no effort other than hooking up all the cables and the displays.

Now, I have the same possibility with the new PCIe stuff and a six PCIe slotted motherboard and even more with using the onboard video card (if it has one)

Of course HDMI can allows chaining ... and stacking and other formats. But that is just silly talk.