I don't know who wouldn't use the correct motor oil in their car. I can a imagine a really lazy person saying, "I bought this oil cause it was closer." Or maybe some guy's quirky uncle passed away and willed the guy all his motor oil, and the guy was innocently trying to make the most of his uncle's weird gift.
But if you are pouring motor oils into your car all will-nilly, you should stop. Don't do it for my sake. Do it for the sake of the environment and your car.