Same issue in UK.
My iPhone 6 was replaced 2 times and all of them had same issue.
I also decided to take a closer look to other devices that were available in shop and i notice that all of them had same issue.
In some cases it was more noticeable in some less.
Also notice that some of them had only problem on top right, some both- top right and left.
6 plus seems to have a little better backlight.
But it looks like it is some kind o production problems.
So iPhone 6 is really good. Size is perfect, love better camera with cool video stabilisation.
But unfortunately backlight uniformity problem was distracting me almost each time viewing web pages, making me feel like there would be something dirty on my screen.
Hope Apple will fix it soon.
Fingers crossed.