Battery longevity is so subjective. I've had my Poke3 for half a year and I can't think of a time where I actually needed to charge it. Syncing and developing it gets enough power that I never even look at the battery gauge.
WiFi is the killer for a number of reasons. You would be amazed how much analytics there are in
anything that you run on your device. If you have WiFi on the app makers will consider it as free to use to send (literally) every click you make back to the home spaceship. The Kindle case is well known. The NeoReader doesn't seem as bad. This is what I found in the Nook Glow reader just with a grep on "lytics".
Code:
Crashlytics
FirebaseAnalytics
Localytics
OmnitureAnalytics
Nah, it's not paranoia, I just don't want them treating my device/WiFi as if they owned it. Just don't look at the logcat of your cell phone, it will drive you crazy all the crap going on there.
I've done actual current measurements on devices but you have to open them up and interrupt the battery lines. It's a drag.