while it's nice, i'd argue e-readers use so little battery that even the default should last for at least a decade, but having it is awesome for sure.

Meh. I would say that if anything deserves an exception, it's ereaders.

Im my wife's kindle PW I can replace the battery, and have done that.

But there are simply no new batteries for that kind of device to be found. So then the new battery lasts 20% longer than the old one, and maybe added a year to the device's life.

Replaceable battery isn't worth much if you don't have a reason to believe you'll be able to source a good one a decade from now.