The only reason the older phones are brighter is due to light leak. The newer phone have higher resolution, better contrast and more accurate color reproduction.
So wouldn't that mean the screen cap isn't Retina. Retake a screenshot on the retina display.
Funny how the carrier information changes in that single "screen capture" from device to device...
Its a screen cap I had stored on each phone for comparison from a backup.
Here is a comparison between the first generation iPhone and the iPhone 4S. They are both set at the same brightness level, yet the original iPhone has a brighter and much more vibrant screen. What does the iPhone's screen quality(not resolution) seem to be getting worse?
Image