Big, Bigger, Biggest

At the corner coffeeshop, coffee drinks come in three sizes: Short, Tall, and Grande, in increasing size.

Short is smaller than Tall. This makes perfect sense. But why is Tall smaller than Grande? Tall means big. Grande means big. Is an Italian big bigger than an English one? I think they should take the idea further, and just use the word for "large" in all different languages, and distinguish between them based on the average size of that country's people. So Okii (Japanese) would be smaller than Big (British accent) would be smaller than Big (American southern accent).