What excellent luck. ARGH!
Wait, I just checked my U.S. copy and I'll have to change my answer to "I've never that noticed before". My borders don't line up either, just as you described; so hopefully that'll make you feel a little better. My U.K. copy has the thinner border on the top for both boards and the fatter border on the bottom for both so it lines up perfectly.
It's also interesting that the GB copy is smaller than the U.S in both board and vehicle size: