The Kindle Paperwhite has a very blue tinted light. I'm not sure about other lighted eBooks, but I dislike that they specifically called out light emitting vs reflective surfaces. As far as I'm aware the colour of the light makes a much bigger difference to melatonin production than the source of the light.

EDIT: Looking at the actual paper they were definitely aware of this with measurements of the colour spectrums of different tablets, unfortunately not including the Paperwhite. Disappointing journalism skewing the story as normal.