Thanks, everyone, for pointing out the "accident of history".
This is a little morality tale about clever programming.
Joe Ossanna would never have tokenized \s constructs that
way if the CAT typesetter had been capable of a wider
range of type sizes. Brian seems to have kept it for
backward compatibility. But groff was perfectly willing
to break backward compatibility in tokenizing command
names. Why not in \s?
I encourage Branden to go whole hog and let
\s123DEWEY WINS produce a banner headline.
Doug