I think the answer is simple. AD attacks! I'm no football Medical expert but...

Anyone who is charging has got to have a less chance of injury than someone playing in a defensive mode. Walter Payton was a good example. HE laid the lumber on Defensive players and was rarely injured, even with a CRAP O line / team around him for most of his career. I look at our O line....They are mostly in Pass Pro...much more of a defensive / vulnerable mode. I'm not saying it makes you invincible but I bet it sure doesn't hurt a career.