I think a lot of people don't get what "billionaire" really means. Chatting to a neighbour yesterday, they mentioned that the owner of their company is a "millionaire or billionaire or something..."
When I said that those are two very different things, they just looked at me quizzically.
They got the difference when I put it like this:
£1 Million stacked in £20 notes is as high as your house.
£1 Billion stacked in £20 notes is almost 4 miles high.
That one letter makes all the difference.