The big difference here is that you cannot remove the battery from apple handhelds or tablets. Thus, you cannot ensure that the unit has no power. They could install a stealth program that makes it look like you've run out of power, remain "on" but inactive except for sending whatever info that they wanted to obtain. Location, sound, video, data - all without your knowledge and while thinking that the phone was out of power, so couldn't be doing any of those things.
http://www.macrumors.com/2014/07/22/appl...