The Imperial System is the American (and British, so I can only assume it started in Britain) system of measurement (inches/feet/yards/pounds (though in Britain, it's stones)).
In 4x03 "Reunion", one of the Satedan guys claim that the legends tell of a 7 feet Satedan. So obviously the Pegasus Galaxy knows the Imperial System.
Which means that aliens created it! Probably the Ancients! The Ancients created the Imperial System! All should convert to it!