Actually, there's a massive difference between lighting just the screen and lighting the surroundings. The second will cause lower eye strain: this
has been studied.
Text rendering was an issue on the K2, yes. Amazon's custom rendering solution had issues which have not affected the used-by-many-readers ADE: it's incorrect to draw any conclusions beyond a software bug on a single model of reader. And while the DPI is "lower than magazine", it remains higher than all but a few specialist TFT panels.
And that's not a study, it's an opinion on Slate and a journalism school's website.
This is a study, about the lighting issue I mentioned.