Really? I get spam addressed to ftp, cyrus (the Cyrus IMAP system),
postfix, apache, daemon, etc etc all the time. Those are very common
user names, and (even better for the spammers) their mail is typically
aliased to a group of people. They're probably in every spammers list
of dictionary words to try.
Still, though, even if I'd never expect legitimate mail to e.g. my
proftpd user, I'd certainly not want to automatically discard it. I'd
prefer a default configuration that sent it to root, but that could
easily be overridden.