We're talking about high-wattage things like boilers, radiators, etc., things that use something like 500-1500W an hour, but aren't as advanced as computer hardware (where you can tune everything in the BIOS). Can such equipment, even though it's rated for say 800W, consume more (810, 850, 900, 2000, etc. Watts) electricity? I don't know much about physics, but I think that they can't, because the resistors are protecting them from getting more voltage in, which is a part of the wattage equation.
P.S. Please keep the explanation more on the "words" side rather than complex formulas, as I said, I'm not a physicist, I'm just a guy who has a mild interest in electronics. :)