Firstly we must all understand that retina is not measured in pixels per inch, ppi, its actually more to do with the distance. This is the reason why apple has difference ppi requirements for different products to be classed retina. So lets stick to mobile phones for this thread. Apple believe that for a mobile phone display, around 326 ppi is retina, this is apparently the point where our eyes cannot see more detail if the ppi were to be increased. Of course Apple has increased the ppi of the plus to over 400. Well it was going to be 460 ppi because the software is actually operating at 2208x1242, but being scaled down to 1080p because apple couldnt be bothered putting in a proper 2208x1242 screen. Considering other manufacturers like samsung are now delivering somewhere like 500-600 ppi on smartphones, I mean does it really make a difference? Does it look better to the human eye? I mean companies like samsung are very successful especially their display technology, and surely they would not be putting in 500-600 ppi screens if it did not make a difference? So are Apple missing out with the "low" ppi numbers or does it simply not make a difference?