Personally, i seriously doubt that most of the ones writing those articles have used the iPad, as in more than what was required for the review they wrote. I doubt most of them even own one of the e-ink readers either. What you're seeing is the reiteration of one of the reasons behind the advent of e-ink technology. In most cases a poor reiteration because they don't have a clue and are just re-stating what they saw as one of the cons in one of the other reviews they read before writing their own.
The primary issue for most folks is that they have never learned how to use the brightness level on their computer monitors to adjust for existing lighting conditions and their own light sensitivity.
I have never met anyone as light sensitive as I am. Just asked the wife, says she hasn't either. I am probably one of the few that have never lost a pair of sun glasses, at least not during the daytime... because I am unable to get 2 feet outside the door. Quite literally, I cannot see moving from one lighting condition to another.
This is drastically more important reading text on a screen than it is with watching video. Just think about it, staring at a white lit up screen really isn't much different than looking at a lit light bulb. Between staring at Excel spreadsheets all day at work, plus my home computing habits... imho, if I can learn how to adjust brightness levels, which I do multiple times a day, then anyone else can also.
People are going to be subject to eyestrain, whether it's from staring at a computer monitor, a musician staring at sheet music, or reading a regular old printed book for hours during the day.