Looking at the results another way, the intelligent IE users would have far better things to do than to play stupid, silly games for the BBC, whereas the newer computer users, who haven't found a reason to change to another browser yet, would probably think that having a quiz on the Internet was a novel idea and thoughtlessly dive in.
Users of the newer browsers would obviously do the quiz thinking that they "were" smart enough to have found a reason to change over.
Just a thought which crossed my mind while using IE.7!!!!