Why can't Starbucks sell "small", "medium", and "large" drinks? Well, in China they used to do exactly that! Until 2007, the three sizes were called 小，中，大 (xiǎo, zhōng, and dà) or small, middle (sized), and big. Close enough! Not that I am defending these global purveyors of mediocre coffee, but the reason for sticking to SML for so long in China is interesting.
One of the biggest deals in Chinese culture is the system of guānxi or connections, and just below that on the chart is the idea of face or miànzi. Many Chinese will literally walk twice as far, spend twice as much, take twice as long, to avoid losing face. Losing face can be saying the wrong thing, arriving early, arriving late, offering to pay, not offering to pay - there are myriad complex rules that interface with the rest of the wonderful, fascinating, ancient thing that is Chinese culture. And so any restaurant or coffee house which required people to know a set of codes to order up standard variations like the size of your cup would be doomed to commercial failure. The risk of not knowing what to call the food you wanted, and losing face, would simply be too great.
This makes it very easy, once you can describe food, or at least rattle off the main ingredients in Mandarin, to get fed in China. You can go to literally any restaurant and say the Chinese equivalent of "Waldorf Salad" (Pāi Huánggua - Smashed Cucumber, and that's exactly what it is) and it comes just as you expect. So rocking into Starbucks for a "S/M/L cup of coffee" works fine, in China at least.
And you know what they call a Big Mac in China? No, not a Royale with Cheese you cheeky thing! It's actually called a Tyrannosaurus Rex (in Mandarin that's Jùwúbà). If anyone knows why, this writer, for one, would be fascinated to be let in on the secret, as everything else in your local Chinese golden arches is called exactly what it is! I only want a small Coke with my chicken burger thanks, and hold the suggest sell.
But finally, thanks to both the extraordinary penetration Western fast-food purveyors have made into the Chinese market, and the local perception of such places as relatively expensive places to eat (I kid you not!), marketing language is now starting to take hold even in this last bastion of calling a spade a spade. Post-2007, the three sizes in China are "middle (sized)", "big", and "especially big" (your translation of the last one may vary). All good things come to an end!
Thanks again to tongpoo for the list of ascii codes for pinyin.