Measuring Marijuana around the world~!!

Ok, we all know that weed is measured in about two different ways. In ounces or fractions of an ounce, or in grams. Now one thing that has stricken me as odd is that people in Canada and the UK and other places that use the metric system will still describe weed measurements in fractions of an ounce. This confuses me. If the whole country is metric, why would you measure weed in the old fashioned U.S. way? I live in the U.S. and where i am its usually only measured in fractions of an ounce. I have never heard anyone who lives near me measure their weed in grams. Has anyone else noticed this and if so what are your thoughts on it?