The story I heard was that the English sizes actually have a simple physical basis (don't know if the others do). Although the sizes may have altered slightly over time, they were based upon the size of some king's foot (possibly Henry 8th, as he claims a lot of things). The length was 13 inches and that became a size 10. Each size bigger/smaller was 1/3 inch different.
UK mens/womens standard sizes are now slightly different in dimensions other then their length.
Also, I think US mens is equivalent to UK mens, though their standard is a bit narrower than the UK equivalent.