I'd like to say, I don't think there's any need to have a screen resolution over 1920x1080 or at most 1920x1200.
These devices are for media consumption, right? Photos will look fine, and all the video media will be formatted for 1080p, so anything higher is excessive.
Keep in mind too, the higher the resolution, the harder the graphics chipset has to work for animations.
AND as somebodyspecial said, text gets very granular, hard to read for some people. High detail is great, but the higher resolution you get, the more you have to customize the fonts to be readable.
Caveats aside, more for the same price or less and improvement is never a bad thing. If the companies keep their entire target audience in mind, every generation they release will do very well.