I was shocked by this when I started attending games annually years ago - I've never been there when it's been full. Not even the game I saw against New England and not for the playoff game I saw against Jacksonville. It seems...odd.
However, the amount of Black and Gold in the stands at EVERY away game is something else. It's pretty incredible. Also, the game day experience at Heinz Field is worlds better than the other venues I've witnessed NFL action (Philly, Baltimore, Cleveland, and NY Giants) Only thing better in my eyes for Game Day experience is in Happy Valley...