Is Rule 13 interpreted more narrowly in non-constitutional litigation than in constitutional cases?

In Authorson v. Attorney General of Canada, 2001 CanLII 4382 (ONCA), McMurtry C.J.O. quoted Dubin C.J.O.’s ruling with approval and further stated (at paragraphs 8 and 9): 8. In contrast [to constitutional cases], Ontario courts have interpreted Rule 13 more narrowly in conventional, non-constitutional litigation. . . . Intervention of third parties into essentially private disputes should be carefully considered as any intervention can add to the costs and complexity of litigation, regardless of an agreement to restrict submissions. 9. Many appeals will fall somewhere in between the constitutional and strictly private litigation continuum, depending on the nature of the case and the issues to be adjudicated. In my view, the burden on the moving party should be a heavier one in cases that are closer to the “private dispute” end of the spectrum.