HarryT is completely spot on. The beauty with eInk is that the only CPU work being done is the original rendering of the image to the screen, then it goes into standby. The processor goes into "hibernation" where it can remain for many many days and the page will stay continually on the screen with very minuscule power drain.
Also, the screen on an eInk display only needs power upon picture change. Hence why you get that slightly annoying flicker on page change. It wipes the screen (per se), and then displays the new rendering. It's very similar to an etch-a-sketch.
With LCD it has to display constantly, at a high refresh rate to even maintain something close to the eInk display. Enjoy that 5 hour battery time
You can compare it to your mobile phone. Does your LCD stay on for days at a time, or does it go to sleep?