XL- Not a great regular season. Finished with all the wins that we needed, entered the playoffs as a 6 seed. Still, nobody said the Steelers would get past the Bengals. Nobody said the Steelers would get past the Colts. Look at that, they did the seemingly impossible.
XLIII - The season of perhaps the most difficult regular season schedule in a long long time. Again, nobody said the Steelers would be able to do what they did that season, and they finished out with 12 wins. That was the regular season and not the playoffs, but I put it in the same category. I also don't recall many "experts" saying that we could beat the Ravens for the 3rd time in the AFCCG, but we did the impossible again in that case.
Ergo, the playoffs are a whole new season. I don't care if we lost to the Pats 100-0 in the regular season. There's no telling what's going to happen once we face them at a different time in a different environment. That is, if we do end up having to play them.
Sooo long story short, that's how we should all know that.