I think it's sort of interesting to look at the actual usage stats and see that there are 4 steel pokemon in the top 6 - Scizor, Ferrothorn, Jirachi, and Heatran, in that order - and then nothing else until Forretress down at 17, and Skarm down at 24. It's an interesting point to note that with Dragons and Steels especially it's only a very small number of pokemon with the actual typing that dominate. So to what degree is it because of the steel typing, and to what degree is it that these pokemon are simply really good? Let's be honest here, when you talk about a defensive steel type, are you thinking of anything other than Ferrothorn, Skarm, Forretress, or Jirachi? Maybe Heatran? Other responses: Yes. I think SR is incredibly important to this concept. IIRC Slowbro is a good example of this atm, with regards to being able to take an Outrage. Aerophoenix: I'd like to suppose that at least partially, the commonness of the types capable of hurting steels is at least partially in part due to the existence of Steels. Fighting was a terrible type in Gen I, because the most powerful typing was Psychic. In Gen II, Dark and Steel were added, both of which beat Psychic and lose to Fighting. And now Fighting is one of the most lauded types in the game. nyttyn: Grass is an interesting type, because of course, Ferrothorn is at #3 right now, and loves its grass typing. Grass has representatives all over the place, and a few of them are certainly noteworthy in their own tiers. Ferrothorn needs no explanation. Ferroseed does well itself in LC. Venusaur is terrifying when it gets out in the sun. Tangrowth is a very effective wall down in the lower tiers, Roserade is great in UU, Shaymin-S.... is Shaymin-S. Celebi also fills a variety of potent roles. Grass isn't a dominating type, but it's not ice, either.