Why can't you charge while device is off?

Every electronic device I have owned, whether it is a dumb phone, portable radio, or smartphone with the exception of Apple allows you to charge your device when it is turned off. Yet, with Apple, you have to charge it while it is on. When I charge it overnight, it is completed within a few hours but it is still on (sleeping). This is causing the battery to drain even more than when off.

While it is true that batteries will lose their charge no matter what, wouldn't it make more sense to allow to charge the phone while off, like all other devices made so when you turn on the phone, the device has the most possible battery charge unlike the way it is now.