Because British money is fucked.
I like the shape of 20p though.
Also it's easier to tell them apart without having to take everything out of your pocket.
Why is the 10p coin bigger than the 20p coins?
Why is the 50p coin bigger than the £1 coins?
i'm not sure. it doesn't really make much sense as 5ps are really small... and 2ps and bigger than 1ps, which are the same size as 5ps i think
It looks like it is all made of the same metals. Is it?
In American money, a long time ago, pennies were made of copper, nickels were made of nickel, and dimes, quarters, half dollars, and silver dollars were all made of silver, so that is why dimes, which are worth ten cents, are smaller than pennies and nickels, which are worth five cents.
Now pennies are copper clad zinc, nickels are still a nickel alloy, and the other coins are a silver colored alloy of nickel and copper. Now we have weird dollar coins that are a yellowish color, but are about the size of a quarter. Our money is crazy too, I think.
http://en.wikipedia.org/wiki/United_States_coinage