They can maintain that "retina" claim as long as the marketing department gets away with it. I think they can easily get away with that down to 200 pixels per inch or so (anecdata: I am myopic, but cannot really see the individual pixels on an iPad 1 Or current iPod touch)
I guess that the extra wiring needed for retina resolution means that you need more backlight to get the same display brightness. If so, one way to market a slightly larger display with say 250 pixels per inch would be by stressing it as having better battery life ('easier to see for the elderly' would work, too, but such a line does not fit Apple's image well)
I guess that the extra wiring needed for retina resolution means that you need more backlight to get the same display brightness. If so, one way to market a slightly larger display with say 250 pixels per inch would be by stressing it as having better battery life ('easier to see for the elderly' would work, too, but such a line does not fit Apple's image well)