My thought has always been that Mr. Lerner is making the point that these are "legal" and not "natural" laws in order to allow Arthur to emphasize his importance in the scheme of things in Camelot. All of the laws adduced apply to natural phenomena over which the king in most worlds doesn't have authority. "Regal" would work here to be sure, but the redundancy brings the point more directly to the hearer's attention. I can imagine it slipping by if regal were used.
