Here's the underlying issue. (It's remarkable how seldom this gets mentioned -- as with reasons behind many other cooking instructions. A 2006 newspaper article even claimed there was no reason to preheat a gas broiler -- which is misleading, and inexplicable since its author was a retired chemistry professor purporting to advise on kitchen science. At least when I took college chemistry, concepts like heat capacity and specific heat were considered important.)
Two heat sources warm food in a broiler: The flame or heating element, and the hot oven surfaces around it. If you use a broiler without preheating, you get only the first source, and the intensity of heat on the food will gradually increase as the oven metal's thermal mass rises in temperature and begins re-radiating with an infrared-rich, so-called "blackbody" spectrum. For the several pounds of metal partaking in this process (in a typical oven), raising the temperature from room to a useful 450-500 F requires that the metal absorb a certain quantity of energy (measured by the metal's "heat capacity") from whatever heat sources are operating. With practical broilers it takes a few minutes. That's what broiler preheating is about.
My electric oven has a "broil" button which turns on the upper heating element. I don't know what temp it clicks off, but when I broil I generally leave the door slightly ajar so the upper heating element never clicks off.
For me, broiling is cooking with the heating element on the entire cooking time. Grilling from above, as Alton Brown described broiling.
When I had a gas stove, the dail also had a "broil" setting. The broiler compartment was at the bottom of the stove below the gas flames. However, I never paid attention if the flames stayed on the entire time or not.