The real reason for leaving the door open on an electric stove when broiling has to do with the oven thermostat. Broiling depends on continuous radiant heat. If the door is closed, the oven compartment will heat up to the point at which the thermostat will turn off the heating element. If the door is left open, the oven never reaches the cut-off temperature, so the heating element stays on through the entire broiling process. Or so my mother explained to me when I was a young and inquisitive sprat.