I have to agree with the OP here... I went to the Apple store today and saw ALL new iPads and iPhone 4S'es were milky white with a slight blue tint [ which looked beautiful and bright ]
My new iPhone 4S and the new iPad had a bit of uneven yellow tint. So, obviously like most of us, I wanted to exchange but kept wondering why ALL Apple store units are cooler!
I had them open 3 iPhones and 2 iPads and they were all the same as mine! Even the guys at the store didn't have an answer for me. The only conclusion I could arrive at was that since these units at the Apple store are on all the time, the glue [ or whatever is causing the yellow/uneven tint ] cures with usage/staying on and the screen gets whiter.
I have, hence, left my new iPad [ yellowish tint on the right 1/3rd side holding in landscape mode ] on at max brightness plugged in all night and it's only slightly warm [ not hot, by any means! ]
The 4S was still on 5.0.1 so I could JB and install ' color profile ' which fixed the screen in a minute!! Love that fix!