[runeks]

> The definition of a retina display is you can't discern individual pixels at normal viewing distances, so unless you're sitting with your nose against the screen or are using a loupe, you won't be able to see a single dead pixel.

Your conclusion does not follow from your premise.

Just because we can't identify individual pixels does not mean a single pixel has no influence. It shapes the overall picture.

If a single dead pixel is not visible at all, why have that pixel there in the first place -- working or not?

I just tested with my iPhone 6 (a 1334x750 px white picture with a single black pixel in the middle of the picture), and the single black pixel is definitely visible. A screenshot of the iPhone showing the picture in question confirms it's a single pixel on the screen.