Yeah, the risks mainly come with extension cords, like plugging a bunch of 10A appliances into a single 20A outlet via a 10A rated extension cord with multiple 10A outlets.
Appliances themselves with their own input fuses and captive cables are less risky, although some kind of internal wiring short could still get all melty.
It's true that sizing the plugs that way does prevent you from plugging a 20A appliance into a 10A extension cord, which makes sense.
