I agree. I think there is always a bit of nerves especially early and a feeling out period similar to a big title fight in boxing that doesn't get going until after the first few rounds. That definitely favours the defense.

I also think coaches/play callers become a little less aggressive in the Super Bowl (especially early). They feel like they need to slow the game down and possess the ball for long stretches. Every possession is so valuable and it is unlikely you will win if you have a bunch of turnover or are giving the other team great field position. I think a lot of coaches/play callers try not to lose instead of going all out to win.