People seem to think that the decision was only down to putting a retina screen or not...
The reality is, that in order to put a retina screen in there, even if possible, would mean a hell of a lot more compromises.. The screen would have consumed a lot more power, it would have needed a lot more gpu power, drawing more heat, and needing even more power, which would have lead apple to increase the battery capacity, making it thicker... And keep in ming that they need to be able to produce something like 15 million units before christsmas...
I would love to see if people would have been able to accept such compromises.. I certainly wouldn't.