Guys, if you know anything about an LCD production, you should also know the problems you're describing will not go away within current technology process. Problems with different hues/tones on different areas of the screen are strictly associated with only jus one LED diode backlighting the whole screen. If the screen was backlighted from all 4 corners, none of those problems would have accured. Moreover, iPad 3 is no exeption. The same thing is with iPhones, iPod touches since 1st generation of these devices. Also, the problems you described occures on most laptop screens and average to good desktop PC monitors. It's just less noticable on them, because the screen is bigger.
So what the iPad is 499$+? It's a mass product device. So called "retina display" is just a marketing term. Besides higher than average dpi iPad's screen doesn't incorporate any special quality. They're average IPS displays at best with lots of imperfections on default, and they are not individually calibrated. Do not expect pro-quality perfect LCD in a 499$+ device in which LCD panel is just one of many components. It's got to be cheap in production. Otherwise an iPAd would start at 1000$+.
You can really save your nerves and be prepared for iPad 5,6,7 etc, because as long as there will be only 1 LED diode for backlight, the hue will be slightly different on many areas of the screen. I assume they chose only 1 diode to not only save manufacturing costs, but also to save battery consumption in already power hungry iPads. It's impossible to manufacture perfectly uniform, clouding-free, 100% perfectly even hue with just 1 LED diode. This is the number 1 reason for most of the screen issues you're describing. So if you're that picky OCDs fine be ready to swap hundreds iDevices in next generation and next and next and so on... until you find that one closest to perfection