Oh and don't forget that the Brits don't entirely use the Metric system either. They use a bastardized system of Metric, Imperial and bits from systems even more archaic than Imperial.
Stone is part of the imperial system, it's 14 pounds. Also, no-one apart from maybe people who use the metric system for their jobs take the piss out of America for using imperial. We use it all the time, beer and milk is in pints, babies weights are announced in lbs and ozs, road signs are in miles and loads more examples I can't be bothered to type as I've said this so many times on this site
Like stone. Wtf!?
It's a result of being arguably the oldest (or one of the oldest) cultures around