Does this article hold water?
It's beren a long time since my degree, but it seems to me that the kindle maintains the memory state irrespective of whether there are books stored within it. Although one could imagine a computer memory using a scheme such as run-length encoding, or at least switching off entire chips when they are all zero, this is not how it works. The entropy of empty memory is the same as that of full memory under most designs.
Furthermore, flash does not use energy to maintain state, so there is no energy difference between a zero and and one. Is there?