In my experience all LCDs have some form of uneven backlighting
It is funny because if you watch the IMAC video the guy goes on about how LED is supposed to provide uniform brightness across the screen.
http://www.apple.com/imac/the-new-imac/#medium
The reality is something different.
I have a lot of experience with LCD TV using the backlight and none of them have even backlight. They all have some defects like spotlighting, uneven backlighting, etc. That is because they both have backlights whether LED or CCFL. You may get one that is better than another but they will all have some kind of anomaly. There is no such thing as a perfect one, despite what you read. It is just inherent in the technology and many factors can cause these (Screws too tight on the bezel, LEDs that don't work or output a different light intensity than its neighbor, etc.). CCFLs can have differing amounts of gas in them and will light at different intensities also.
The only technology that will give you a uniform screen is CRT or Plasma. There are no exceptions.
That is why the best displays will always be CRT first and plasma a close second. Don't believe the marketing hype, plasma will always be a better technology than LCD. It is just too cost prohibitive and uses too much power for computer monitors.
So, give Apple a break, they are only using the best of what is made and any other manufacturer will be no different.
LG makes these panels and is one of the largest panel makers out there. I do believe that these are quality panels, but still think that the backlight is what makes (LED or CCFL) LCD bad. Until LCDs can provide their own light for each pixel (like a phosphor) they will always have these defects.