Uh ...
How much do you think a Billion is?
In Europe, most people would say it is million millions, that is 1 000 000 000 000 or 10^12
In USA, however a Billion is a thousand millions, that is 1 000 000 000 or 10^9
Could that be a reason why there are many more billionaires in USA
See
http://en.wikipedia.org/wiki/Long_and_short_scales