Yes, Ben is right there in the top group. Tough SOB and makes big plays in big spots. But the Steelers win because of their defense. Look at their years since 2001:
Year: record, Def Rank (pts), Def Rank (yds), Result
2001: 13-3, #3 pts, #1 yds, lost in AFC Championship game (to NE)
2002: 10-5-1, #16 pts, #7 yds, lost in divisional round
2003: 6-10, #15 pts, #9 yds, missed playoffs
2004: 15-1, #1 pts, #1 yds, lost in AFC Championship game (to NE)
2005: 11-5, #3 pts, #4 yds, won Super Bowl
2006: 8-8, #11 pts, #9 yds, missed playoffs
2007: 10-6, #2 pts, #1 yds, lost in wild card round
2008: 12-4, #1 pts, #1 yds, won Super Bowl
2009: 9-7, #12 pts, #5 yds, missed playoffs
2010: 12-4, #1 pts, #2 yds, have advanced to the Super Bowl
So their best years (2001, 2004, 2005, 2008, 2010) they had essentially the best defense in the league. When their D slipped (never to a bad level, but just to a merely "good" level), they didn't do a heck of a lot.
Yes, the Steelers have always had a great defense and some years are better than others. But for me, the difference is Ben. Did they win Superbowls with Tommy Maddox, Kordell Stewart, or Neil O'Donnell? Still had great defenses and running games back then. O'Donnell made it to the SB and lost. Maddox and Kordell never even made it there. Ben's going there 3 times in 6 years. He's elite.