I’ll list the Steelers’ injuries, and you’ll say that good teams are built to fight through massive, potentially crippling injuries. You’ll do that while pointing to this year’s edition of the Houston Texans, and last year’s world champion Green Bay Packers.

You’re right, and for the 2011 Steelers whose season ended tonight after an overtime loss to the Broncos, injuries aren’t a sufficient excuse. They’re reality, and perhaps an increasingly dark reality that could see the window of opportunity for an aging team begin to close.

Ben Roethlisberger entered this game hobbled, and although we saw the old scrambling Big Ben who’s creative and inventive outside of the pocket in the second half, his inconsistencies in the first half were a major factor that led to Pittsburgh’s deep and surprising hole 20-6 first half hole.

This was a game in which the opposition’s quarterback was both a hero and an anomaly, and an unconventional passer with a reputation of doing little passing, and a lot of missing.Yet midway through the second quarter, Tim Tebow had completed 50 percent of his passes–which is about on par with normal Tebow standards–while Roethlisberger was toiling at a meager 42.1 after completing 63.2 percent of his throws during the regular season.

In the end, though, Pittsburgh’s first-half deficit could have meant little had it not been for a botched snap by center Doug Legursky with 29 seconds left in the second quarter. With Roethlisberger in the shotgun, Legursky fired the snap past his unprepared quarterback, resulting in a 23-yard loss. The Steelers were on Denver’s 32-yard-line, and poised for a field goal attempt that certainly wouldn’t have been a gimmie, but would have been far easier in the thin Rocky Mountain air.

Legursky occupied that important piece of starting real estate due to the absence of Maurkice Pouncey, a highly-talented second-year center who made the Pro Bowl as a rookie, and again this year. But over two seasons Pouncey’s now missed two vitally important playoff games between today’s loss, and last year’s Super Bowl.

Pouncey’s absence forced Chris Kemoeatu into the game after Legursky slid over, and the mistake-prone guard was making just his second start over Pittsburgh’s last seven games. Throw in Max Starks’ injury, and the Steelers’ age and Pouncey’s injury-prone ways led to a patchwork offensive line in front of a weakened Roethlisberger. With a fully healthy line, Pittsburgh’s averaged six more points per game.

Kemoeatu and Starks are both 29 years old, and Roethlisberger just completed his eighth season while playing behind an offensive line that gave up 42 sacks. That’s the kind of advancing age that will slowly shut that Steelers window, and lead to more missed games and hobbled outings for their offensive anchor.

For much of the game those holes up front didn’t have much impact, because until the dying minutes, Denver’s pass rush created little pocket turbulence. But that performance was reciprocated by the Steel Curtain that was instead reduced to several sheets of calming and comfortable silk. James Harrison and LaMarr Woodley vanished, and when Tebow was in the grasp of a defender he often squirted free. The only saving and nearly game-changing grace for the Steelers was Ryan Mundy’s hit that caused Willis McGahee’s fourth-quarter fumble.

Tebow’s running wasn’t surprising, but his ability to throw against the league’s best pass defense was downright staggering. Propelled by the absence of a pass rush, Tebow threw for 316 yards, the highest single-game yardage total of his career.

Beyond the yardage total, what was even more shocking was the amount of deep passes surrendered by Pittsburgh. A secondary that had given up only two receptions of 40 yards or more throughout 16 regular-season games coughed up four today.

Put another way that leads to even more shock, awe, or depression depending on where your fan affiliation falls, Pittsburgh faced 530 passes during the season, and only two of them resulted in a completion of 40 yards or more. They faced 21 today, and gave up three.

Blame it on the injuries, or the hobbling that resulted because of those injuries if you want to salvage sleep, Steelers fans. But between Harrison (33), Troy Polamalu (30), Brett Keisel (33), and Casey Hampton (34), what we witnessed today was an elderly defense done in by a lack of durability due to their advanced age, and dominated by a combination of youth and offensive innovation at the NFL level. Hampton and Keisel also left with injures, leaving the Steelers with only three healthy defensive linemen.

Pittsburgh is still one of the AFC’s elite teams, but the youth of Denver, Houston, and Cincinnati is quickly closing that gap.