This is what helps me....
Ok, I've attended 2 AFC title games - the '04 (season) in Pittsburgh and the latest one in Foxboro against the Chargers. In one matchup you have the Pats going into the house of potentially one of the greatest teams ever (let's give Pitt credit, they were damn good that year) and in the other we hosted a severely banged-up Chargers team.
The '04 Pats, save for the hiccup in Miami, played dominant football down the stretch and just dominated one of the best offenses in NFL history. The '07 Pats, played in a lot of nail-biters and managed to pull away from Jax.
In the first half in Pittsburgh, NE played one of the most impressive half's of football I've EVER seen by ANY team. Nothing the '07 Pats did all season even came close. In the AFC title game, NE let the beat-up and (LT-less) Chargers hang around and finally closed the door in the closing minutes.
My point being- even though the '07 Pats had 18-0, they weren't playing at the level they needed to at that point. And this was clearly evident in the Super Bowl. The Giants' momentum was just too much.