5" is too large for some people, and they talk about the resolution, and I don't find it unreasonable to make the statement that 300 dpi is good enough, and that higher resolution is mostly just decreased battery life (the screeen power consumption and the processing needed for the extra pixels)
At some point, the idea of a super high resolution screen with small dimensions really doesn't make sense.Is that point 300 dpi? if not, what is that point?
300 dpi is the point where printed material is considered 'good enough' for professional use (I remember quite well when it became possible to buy home printers that could do 300 dpi)
The kindle with it's "great" screen is only 167 dpi, most desktop/laptop displays are around 100 dpi, with their "retina" displays (supposedly the limits of human eyesight according to their marketing) around 220-260 dpi
I carry three devices around with me all the time. a Kindle DX (9.7" 150 dpi), a Nexus 10 (10" 300 dpi), and a HTC One (4.7" 468 dpi). I would MUCH rather read on either my Nexus or my Kindle than on the HTC.
It's going to be interesting to see if they can do this, or if the "higher numbers are better" marketing hurts them. Unfortunately, I don't have the money to try this right now.