SI and "the metric system" are not equivalent, just as EES and "those bass-ackwards Americans" are not equivalent. SI is a subset of available metric units -- or more specifically, magnitude prefixes. EES, for example, does not use gallons for a measurement of volume, but rather cubic feet. SI does not use hectograms, which is a common and convenient way to sell meats and vegatables on the Continent -- SI uses grams or kilograms or milligrams. One goes from millimeters to meters to kilometers. Centimeters are convenient for common metric measurements, but strictly speaking are not allowed in SI.