>>> ... miles, inches, feet and yards, ..., a sort of English, because yes - you guessed it - we were your colonial masters.
Up to here you are absolutely correct
>>> Somewhere along the way you lot got a bit bolshy, and changed the fluid measures.
I am sorry to disagree with you but IT IS AGAIN because New World colonies were under Empire's control at that time. When U.S.A. rebelled against the mainland the number of measures, all called gallon (!) were in use - wet, dry, grain gallon, etc. Because each one of these was measuring different ammount (even some volume were by volume while others were by weight), so Queen Victoria set the new Imperial gallon, now sometimes referred as UK gallon. U.S.A. were "sticking to traditions" all over their long-long (2 centuries) history, so are still using the gallon from 1780s. The latter is rather incorrectly called US gallon, while it is still an UK gallon but an obsolete one!
P.S. Dear Befuddled American, please learn some history and educate yourself. Contrary to the widespread belief in U.S.A., even the democracy WAS NOT invented in your homeland! Actually Magna Carta was "invented" / "discovered" (maybe just written) guess where - yeeees, good job, in Great Britain indeed.