The convention of using relatively-short service-based host portions of an FQDN pre-dates the WWW. It was common to use mail, gopher, irc, whatever for various

The convention of using relatively-short service-based host portions of an FQDN pre-dates the WWW. It was common to use mail, gopher, irc, whatever for various servers from a functional point of view. Whether it was an A record or a CNAME record was generally at the adminstrators preference. CNAMEs had their own hiccups and weirdness to deal with, and still do to a lesser degree.