For me it comes down to using the graticule scale on a chart for measuring distance. One minute of one degree of latitude equals one nautical mile, therefore the use of knots makes perfect sense.
27/09 I think you will find that's the geographic nautical mile (which as I am sure we know varies in distance over the earth since the latter is an oblate spheroid).
The International Nautical Mile, last time I checked, is defined as 1852 metres (no doubt the eurokrats got their hands on this definition!).
That said I agree with your reasoning for sticking with nautical miles and knots - "miles per hour" was an awful American invention.