The Hacker's Dictionary says that daemons were so named in CTSS. I'm guessing then that Ken Thompson brought them into Unix? I've noticed that more recent implementations of init have shunned the traditional terminology in favor of the more prosaic word "services". For example, Solaris now has SMF, the Service Management Facility, and systemd, the linux replacement for init, has services as well. It makes me a little sad, because it feels like some of the imaginativeness, fancifulness, and playfulness that imbue the Unix spirit are being lost.