Let's look at the RBs to recently face the Steelers' defense:
wk13 - cin - Rudi Johnson - 98 yards, 2 TDs, 4.7 ypc
wk14 - chi - T. Jones - 72 yards, 1 TD, 5.1 ypc
wk 15 & 16, shut down the Vikings and Browns' running game.
wk 17 - K. Jones - 78 yards, 0 TDs, 4.3 YPC (Kevin freaking Jones?)
playoffs
@cin - Rudi Johnson - 56 yards, 1 TD, 4.3 ypc
@ind - E. James - 56 yards, 1 TD, 4.3 ypc
@den - Anderson/Bell/Plummer - 97 yards, 1 TD, 4.6 ypc
Common theme - just about everyone that runs against the Steelers' defense has good ypc, but some have abandoned the run. Opponents also are getting rushing TDs.
"So how come the Steelers have surrendered just 3.4 ypa for the season?"
Because their run defense was far better earlier in the year:
wk3 - nwe - held Dillon to 2.8 ypc
wk4 - sdg - held Tomlinson to 3.4 ypc
wk8 - bal - held Lewis to 3.6 ypc
wk9 - gnb - held Gado to 2.4 ypc
wk10 - cle - held Droughns to 3.3 ypc
wk11 - bal - held Taylor to 3.1 ypc
They haven't been stopping the run nearly as well in the last couple of months, and their rush defense numbers have been slipping. Contrast that with the Seahawks holding Portis to 2.4 ypc in the second round.
Now this suddenly suspect run defense is gonna meet the best OL in the NFL. Uh-oh.
MVP of the game - S. Alexander - 125-150 yards 2 TDs.