I know this is common knowledge now, but just for people who might not realize it: a typical North American NEMA 5-15R receptacle will indeed deliver 120V 15A electricity, but the electrical grid is split-phase 240V. Right across from my dish washer is an electric range; most of these require 240V 30A or 50A receptacles (I think mine is 30A, but I could be mis-remembering.) So it's not like we couldn't have higher power dishwasher, but if you already have central water heating it's kind of senseless to heat the water at the dishwasher.