[Magnesus]

Strange. I had two completely different e-readers (one with old 4 colour screen and one with new 8 colour one) and both had EXACTLY the same contrast.

The pic is misleading.
1) The readers have different colour borders. White border will make the screen look darker and black border - lighter (look for some optical illusions on googe graphics - the effect could be very strong). Also DR and contrast enhancer in photo camera could exaggerate the difference.
2) If you copy fragment of any screen to the one on the Entourage Edge screen in graphics editor you will notice that the only difference is in the part where there is obviously some light falling on the left side of the black device and right side of the middle one. Actually you even see part of the light patch on the top of the black LCD.

Differences you see may also be the reason of:
1) Partial instead of full refresh on some screens (huge difference in contrast),
2) Different fonts (very probable!),
3) Different antialiasing method for fonts (could make letters more gray).