The only cards that can run 3 displays without using the displayport are the 260x,285 and 290 series. The mst hub acts as an active adapter and that is why you can use the remaining ports on the graphic card. Why we don’t have a 4 Hdmi port hub? Hdmi port has a royalty fee and it can make the product quite expensive. Also as dp displays will became more common and also work at 10 bit it will became more popular over time. Note that all mst hubs are dp 1.2a spec, this will make it very useful for adaptive sync displays for gaming design etc