I like the 'allows for about X amount of page turns' statement. Works for printers. But there are factors that doesn't seem to be considered.
I don't have a Kindle or Nook, I have a BeBook, but my problem appears to be universal to these readers as well. If I leave my reader in standby mode, the battery is dead within a few days to a week. But if I use it every night for an hour or so, I can make a couple of weeks on the same charge.