I saw a similar test a while back where people were asked to draw the handicap parking sign. A really simple shape that most people see several times a week if not every day. And many people couldn't even to that. Most people realized their drawing looked obviously wrong, but could not point to what was wrong. As you say, visualizing things, even simple things, is hard for most people.
Just ask a number of people to draw a normal bike and you get all sort of strange drawings, just look at this page: http://bikedrawings.tumblr.com/
It's hard to visualize anything.