When is a Stone not a Stone, and Why?

[Steve]

Just on the off chance that someone from the UK, or possibly the EU, is reading this thread, please explain something to me?

Why do you still use an antiquated measurement of weight as obscure and useless as STONES? (14 pounds, 6.4kg)

If you ask anyone their weight, they will answer in Stones? Do you have bathroom scales that weigh in Stones? Can you buy any commodities that are officially sold in Stones? A stone of oranges? A stone of mince? A stone of rocks?  

If find it odd that people can know their weight in Stones, but not have a clue what that is in pounds or kilos without stopping to convert it? 

So, could someone explain to me how and why this unit of measurement continues on in the modern world? 

Just curious, slightly frustrated, but mostly curious.

Steve/bboyminn