As an electrical engineer, I disagree. Most simple toasters have a single electrical contact that is activated when the bread is lowered. When the bimetal thermostat senses the proper temperature, is deactivates the switch and current stops flowing.

We could say the same for so many products... the toaster is only one. If I use a fridge to keep my food cool and then after I don't need it anymore BUT let it plugged it'll waste energy as well... same for a water heater...

A fridge works on a thermostat switching the motor on and off, so you will save power, but there is no way that a appliance like a kettle or a toaster can consume electricity by just being plugged in because off the bimetal strips disconnecting the live conductor and breaking the circuit, and you need a complete circuit for current to flow. I am a electrician and the testers do not even register plugged in appliances like toasters and kettles.