So how many cell phones do you know that a powered off with a hard switch. You know, flip the switch like you do on your living room light. Or how many people do you know that take their battery out when the power their phone off. Well there is your answer.
Again, how do you know the phone is powered off unless you have a flip switch connected to the battery, take the battery out (and at the same time assume there is other smaller battery in there) ?