> I can’t help wondering, though, why he didn’t use head -${1} in the last line. It seems more natural than sed. Is it possible that head hadn’t been written yet?

I'm not sure when head(1) was added, but I doubt it was added by anyone in the Unix core team at Bell Labs, it certainly didn't make it to Plan 9 because it is redundant with sed as the example illustrates.

sed 11q is concise and clear, no need for shortcuts, but if you really have to, you can write your own head shell script that just calls sed.