The Steelers defense has become very effective this year and it is because they are creating a lot of turnovers. They are also keeping opposing offenses down in the amount of scoring. This is reminiscent of the Steelers of old.
The effectiveness of the Steelers defense during the end of the Cowher era and into the whole Tomlin era has been marked by great outside linebacker play. The defense is effective based on whether the Steelers are getting pressure and sacks from their outside linebackers.
The front four in any defense is the key to getting pressure and the Black & Gold have been able to get pressure from the inside in recent memory.