Well, there are LCD:s and there are LCD:s. And there are eInk and there are eInk screens.
A bad eInk screen (linke the PR600) and a good LCD (like an iPad)-maybe not so much difference.
A great eInk screen vs a not top notch LCD -maybe a different result?
All I know is to get as good reading experience on my LCD devices (Nook Color and Samsung Tab) I have to fiddle around a lot more with settings, turn down brightness a lot and so on to not get eye strain. My eInk devices I just make sure I have a good reading light and I'm ready to read for ever. Don't care how many studies tell me I'm "wrong".