In the image above we have a brief explanation of how WORKS Retina Display technology and how the number of pixels per inch influences the quality of the screen. Notice that above we have a blue dot where the iPhone 4 is placed, which has 300 ppi if the screen is held 0.3 meters from our eyes. As the distance increases, the number of pixels per inch decreases, an iPhone 4 reaching around 100 if we hold it 1 meter from our eyes. The iPad tablet has 132 pixels per inch if it is held half a meter/1 m from our eyes, that is, in the position in which almost everyone holds it. According to the table above, the human eye cannot distinguish the pixels on the screen if the number of ppi is between 90 - 150.
So iPad 2 would not need a screen with a resolution of 2048 x 1536 for us to see quality similar to that of a Retina Display, in fact the iPad tablet already offers this quality if it is held at half a meter/1 m by our eyes. The iPad tablet has a resolution of 1024 x 768, good enough to provide clear images in any conditions, so a doubling of this resolution would be simply useless.
