It wouldn't even occur to me that a plain hamburger would be any different to just the meat and the bun. Guess I live and learn!
I did have a bad habit of ordering a McDonalds cheeseburger with just the lettuce, cheese, tomato, onion and mayo - hold the meat, hold the gerkin, hold the ketchup! I'd say they got it correct around 40% of the time. I tried ordering it so many different ways, didn't seem to matter!