You also have the rematches in Emerald, and the return to Kanto in Gold and Silver (and the rematches of<em>those</em>battles in HeartGold and SoulSilver). I just find it a little strange, though. Not just because it's supposed to sort out trainers worthy of challenging the Elite Four, but because, as mentioned before, that must mean the gym leaders have<em>loads</em>of teams lying around to switch between.