Just warming up the ol' typing fingers...

I know that this is probably well covered territory at this point but, just out of curiosity, when did drinks cease coming in 'small' sizes? I ordered a medium coffee at Dunkin' Donuts (my first mistake...don't trust any place that does the cream and sugar for you. They will fuck it up.) and they brought out this little ass cup. "I thought I asked for a medium, is this a small?" The squat little tank of a woman behind the counter replied, "Yes...is medium" and directed me toward the menu where I discovered that the sizes are now M, L, and XL (shows how often I get fast food.) My question then is, why not just make the medium a small and downgrade the rest of them accordingly? I know it seems like common sense but, well, I think that's in short supply these days...