They aren't the same Steelers because they have a lot of new pieces. Their top WR is out, they have a rookie RB, new C, OL issues, etc. This isn't a case of the offense being in good shape and Ben is just holding them back. Ben isn't what he once was but if he had an offense that he could manage and compliment rather than carry, he would be fine.
What surprised me the most in the game last night was how ineffective the running game was. Maybe that is where Ben's shortcomings are amplified since the Steelers should have been gashing the Seahawks in the passing game with them loading up so heavy to stop the run.
