Except the metric serving sizes are very inconvenient unless you like to do long division in your head.

For example, I have two yogurts, one has 18g carbs per 170g serving, the other has 34 g per 227g serving. Quick, how much more carbs would I have if I ate the same amount?

It's a lot easier to tell if you know one is 6oz and the other is 8oz, or if the servings were designed in metric sizes (e.g. 150g and 200g).