I normally would switch in a Steel-type if I had no prior information on Salamence (or D-nite), which was the situation I thought I was addressing when I made that post. Salamence can dent anything with Draco Meteor, which is it's safest attack. To use Fire Blast is to risk Heatran or a bulky water coming in and stopping you from netting a kill while you've lost 35% HP for nothing (possibly more if SS is in play). And the next time that you would switched back in, assuming you were retreating and not staying in, you would have lost 60% and not killed anything yet. There is absolutely no reason to lead with Fire Blast unless you know that all of your opponents safest switch-ins are weak to Fire. Steel-types are the greatest switch-in in a situation where the opponent hasn't scouted your entire team (unlikely as MixMence is generally an early-mid game Pokemon used for opening up holes in the opponents team) because Draco Meteor will always be the safest bet for Salamence to use, as it dents everything bar Steel types (kind of) and Blissey.
Also, a 2HKO doesn't matter in the situation that a healthy Steel-type comes in after Salamence uses Draco Meteor. If a Metagross with 60% (after SR) comes in after you kill something with Draco Meteor then it's going to kill you unless you CH. If Jirachi comes in with at least 50% (after SR, of course), it's going to kill you unless you CH. Of course this doesn't matter if you were trying to say that you bring in a Steel on the Draco Meteor, but your post didn't really sound like you were trying to say that. If it did, then yes of course it can still 2KHO but switch-ins all depend on the specific situation and the specific team and you can't generalize something like that. I could be sacrificing my steel or I could be using it to lure in a Fire Blast for Vaporeon or Suicune to make Salamence lose more HP, etc. Also I kind of lost where I was going so this post may be unorganized.