I've just finished watching the Discovery channel doco too. It's available from Amazon UK.
I'm not sure if you're aware, but the reason for standards like nautical miles etc, is for navigation as it ties to navigation.
A nautical mile (symbol M, NM or nmi) is a unit of distance that is approximately one minute of arc measured along any meridian. By international agreement it has been set at 1,852 metres exactly (about 6,076 feet).
Try navigating in kilometres, and you'll rapidly get lost.