When designing one of the first thing you learn is safety first. On a device generating heat, having a power button which could easily be forgotten, is a bad idea. In this particular case, the consequences’ can be severe if a user forgets to power off. That is why the power button have been deliberately omitted. Cognitively speaking, it is easier to remember to pull the cord from the jack than switching of a button. You use more muscles and are often forced to use both hands. Using more of your body in an action helps you to remember. The case is the same with an iron.
Iron without power button
This is the reason for not having a power button on non-exclusive heat generating devices. But, there are differences. Exclusive hardware having electronics for safety do have a power button, since it saves the user from error. As in the Sandwich Toaster by taerv:
This sandwich toaster is designed for people who seek high quality and durable home appliances. Thanks to power button there is no need for pluging cable to the socket every time we want to use this device,
and built-in a timer makes it much easier to use. While using you do not have to check the state of the thing we toast – you only have to set amount time you want (shown by shining diods), after which the sandwich toaster turns itself off and sygnalizes that with a sound.
Straight handle and special hinge facilitates compressing thicker sandwiches and steel latch will never break. Heating plates are interchangable so the device is much more functional and it’s easier to keep it clean.