"I don't how a charger can use power if nothing is charging on it"
Because the charger circuit itself needs power, but not a lot, perhaps 10% or so of what it draws whilst charging.
"However, sticking a knitting needle into the connection if it is switched ON will complete the circuit and cause power to flow - THROUGH YOU - to the ground."
I'm not quite sure where you're talking about sticking it, but if it's in the little plug that goes in the phone it won't hurt you for two reasons. Firstly the charger output is isolated from the mains, and from ground, and secondly it's only low voltage.
If you stick the needle in the bottom right hole of the mains socket you will get electrocuted if the switch is on, and you're touching something grounded at the same time. There's a safety shutter in there to stop you doing it though, unless you open the shutter by sticking something into the top (earth) pin.
Kettles and hairdryers don't draw anything when switched off at the appliance. TVs don't cost as much as they used to since they set new lower standards for standby current, my TV costs about 50p a year on standby.