Since an attack is unlikely he's just playing to his own audience. If a real reason for an attack arises he'll change his tune.
Remember about a month ago when Rumsfeld announced US troops would be moved from near the NK border to southern SK? President Roh was very upset at this prospect, he smelled the beginnings of an eventual pullout. You're right, his comments are nothing more than semantics, domestic politics, but if or when the chips are ever down you can bet your last nickle he'll support anything we do.