But aren't our retinas insufficient?
Does it really matter having these super-resolutions when you sit 1-2 feet from a monitor? I thought the whole "magical" thing about the retina display was it was pretty close to maximum resolvable pixel density when held at a distance that you use the phone? As any fule no, the further you are from an image the lower the acceptable / discernible resolution required. Hence magazines are higher dpi than billboards. You see the same effect in reverse when you sit too close to your friend's massive HDTV and see all the jaggies.
So the only need for such high densities and resolutions are if you are sitting close to a massive display?