That is a fair point, although I wonder how long this will hold true considering the ever increasing prevalence of heatpumps, sun-boilers, and other such equipment.
Stuff you should know did an episode on dishwashers and I believe if you washed your dishes for a minute, you've already used more water than a dishwasher. It was pretty mindblowing. They did, though, go through some studies that made it seem that dishwashers were too sterile and getting a little leftover or germ from your handwashed plates was better for your immune system.