The original design of the Glock 30 was based on a shared design for the 10mm Auto. Those that want to shoot .45 Super, 10mm Auto, .40 Super, and .460 Rowland using the G30 pistol frame and slide are very grateful to Gaston for his foresight.
None of those options are feasible with the G30S.
The weight and stiffness of the thicker G30 slide and barrel tame recoil substantially and add to the amazing accuracy of the G30. Some GSSF match competitors put a G30 slide on a G36 frame to reap the benefits of the G30 upper design.