So there is an interesting bit you're overlooking perhaps, which is 'gamut'. The additional pixel density can be exploited to provide "pixels" which have more subtle variations in color. In color printing the printer is capable of some number of dots per inch, but there is another number (sometimes called the 'screen resolution' as a kick back to the silkscreen printing process) where the color gamut peaks (the maximum number of different colors the printer can print). Generally screen gamut in 'sub-retina' displays is fixed by the ability of the electronics to modulate the component colors, but with additional pixels you can 'squeeze out' more colors by using a group of four, or nine, pixels that are colored to simulate a single pixel.

Not a huge deal yet, but no doubt it will become one with '4x' and '8x' oversampled displays.