Sometimes I think that individuals who "expect" a retina screen on ipad3 must not be very good at math.
Why no "retina" display?
1. Screen would be too expensive, especially since the yield rates (ie, defect free screens) are low with that number of pixels. Apple's manufacturers have barely been able to produce 1024x768 screens in the numbers that Apple has needed.
2. Battery life, more pixels to drive, more current demand. Steve is not going to sacrifice battery life to make an even a higher density screen for a $500 device that already has a higher pixel density then his $2000 MBP.
3. GPU. Would require a better GPU to drive decent textures on that size screen. Mobile GPU in laptops with cooling fans are barely up to that task, and craming one of those in an ipad would turn it into a hotplate. Ouch, don't put it in your lap.
4. Apple has finally started to make some headway with getting developers turned on to making HD versions exclusively for iPad. How long do you think it would take to actually get any decent number of apps turned out for the new xHD display? 2013-2014?
5. all the HD apps would look like crap, like iphone apps currently look on the ipad. Would you really pay $$$$$ to buy a "retina" ipad that had maybe a dozen nice looking apps, and 100000 crappy looking ones available?
6. Do you really thnk you can buy a full blown tablet with a 2048x1536 display for $500, when a monitor with that kind of resolution alone will run you $600 today?
7. Retina display is a stupid concept. Sure, an iphone held 10" from your face benefits from high resolution, but the ipad sitting on your lap is already close to achieving "less then 0.6 arc-minutes". It is twice the distance from your face, so only needs half the ppi to deliver the same effect. Ok, ok, the ipad as it exists is only 40% of the ppi of the iphone4 (132 vs 326), but that is close enough.
The really telling point is the whole yield rate issue. Trying to mass produce displays with that pixel density would result in an unsustainable rejection rate of 10-15% of panels, or more. Maybe in 2014, but display manufacturing ech just isn't up to the job yet. Would you be willing to accept 30 dead pixels for the sake of owning a "retina" display?
You want your ipad to have a retina display? Hold it 2.5 times further from your face then your iphone. Mission accomplished.