Originally Posted by DaleDe
That is the number for doubling the resolution but not exactly the size of the minimum needed to achieve a retina result. Of course the minimum size depends on several factors such as the distance from the eye to the display and the acuity of the eye itself such as 20/20 or possibly better. See the article on retina display in wikipedia for more details. There have also been web articles verifying and arguing with the Apple definition. A simple search will turn up many of them.
Certainly true, but apple is most likely to stick to existing screen resolutions rather than introducing a new one (for instance, 1600x1200), as this would require developers to update their apps just to fit in the new resolution (as it happened on the iphone 5). I could well be mistaken, but my money would be on them doubling each axis to make it retina.