If the NHS, clotted cream, and P.D. James weren't enough to keep me in this country, the shopping trolleys would. In the US, shopping carts--or buggies depending on your location--have two caster wheels. It is not only our obligation as Americans to complain about one of those wheels becoming stiff, or full of hair, or not full enough of oil, but also our obligation not to see the easy solution to the problem.
Here in the UK, they have seen the obvious, implemented it across the country, and then failed to send that solution across the pond. When next the two countries take opposing sides in a world conflict, the UK will win hands down on the basis of shopping trolley engineering alone. That's right, all four wheels on a shopping trolleys are castor wheels. And no, I have never ever run into a friend at the grocery store and had reason to whinge about the trolley pulling in one direction.
I attribute this difference entirely to the O in castor being more wheel like than the E in caster.