Nope, there’s no such “requirement.” I stroll in and order a small, black decaf...and they turn over the correct drink. Sometimes they’ll say “room?” and I reply “No, black.” I refuse to play their pretentious word games.
On those exceedingly rare occasions when I go into Charbucks, I just order a small (er, tall) drip coffee. And when the ask if I want "room for cream" I say yes, even though I drink it black. More often than not I'm taking it to go and I'm less likely to spill it on myself while driving.
I can remember a time when they offered a "short" size. Of course I also remember a time when a "small" soft drink at a fast food joint was sixteen ounces, even outside New York City; most places now call a 20oz cup small.