I don't think you get the point. Apple pairs 4/5k panels with sub par gpu's for it's intended native resolution. That's like trying to haul a couple of tons with a Ford Pinto. It doesn't make sense. While it works for watching videos and basic video/picture editing. It will not fare well with games at native or half of its native resolution. Would you buy and Xbox 360 and a 4k TV to play at 4k resolution? I would hope not, as the hardware wouldn't be up to par.
On the PC side of things, a VERY common thing to do is, pairing a GPU with a Display.
See Here. Isn't the whole point of having a Mac, because of its simplicity, and how it just "works"? Why tinker with all the settings? If someone is spending over 3k on a computer, don't you think it should be able to do much more than a PC that costs a FRACTION of the price, yet can run circles around the high end Mac's?