REK confirms that "The Road Goes On and On" was, in fact, a shot at Toby Keith. Apparently (and I had never heard Keith's song, those was news to me), REK is fairly certain that Keith's "Bullets in the Gun" has a melody ripped off from REK's seminal "The Road Goes On Forever."
http://www.tmdailypost.com/article/entertainment/fightin-words-robert-earl-keen-v-toby-keith
http://www.tmdailypost.com/article/entertainment/fightin-words-robert-earl-keen-v-toby-keith