After exchanging numerous iPad 3 units with the exact same screen flaws before finding an acceptable one and after deciding against an iPad 4 because all of the ones that I saw had similar issues, I have learned the following.
1. Screen flaws do not go away. It doesn't matter how long you keep it. I kept one of my flawed iPads for over a month, and the screen flaws did not change or go away.
2. Batches do not matter. Apple buys these screens in huge quantities. They do not buy them in small amounts and they do not scrap parts. It was three months before I got an iPad 3 that was acceptable. And i got lucky. I went through quite a few batches before hitting on this one.
3. Apple will say anything to get you to keep the device you have past your return period. The "settling in" comment is the perfect example. And short of actual dead pixels, they will never admit seeing a screen defect. They may grudgingly give you a few replacements, but it will always be grudgingly.
4. Location bought does not matter. My iPad 3s came from two best buys, three targets, and an apple store. It didn't matter.
5. None of these issues are related to glue drying. Tear downs have proven that glue is not involved.
6. Not everyone will have screen issues and not everyone that does will see or notice them. My father in law's iPad 4 is definitely darker along the left side. He just doesn't see it. I am not going to point it out, because once seen, it can't be unseen.
7. Apple relies on people to accept flaws for the sake of owning the product. If everyone who had flaws chose to reject them, then the sheer number of returns would force Apple to rethink its practices. This same thing can be seen with the retina MacBook and the LG screen ghosting issues. A very expensive device with a big flaw in some of the screens. And not only are people accepting it, but they are spending an additional 289 dollars on apple care, in case it becomes a problem that they can't accept in the future.
I wonder if these flaws are just the result of the technology. I keep seeing the term IGZO thrown around. I was hoping these new iPads would have those screens in them. From what I have read, they are supposed to have more even backlighting.
It makes me sad to see that they continue on the iPad Air. I hope that at least there are fewer problems than on the previous models. I wish everyone luck.