You are mistaken, in the Bucs Super Bowl win, the defense scored 3 touchdowns on interceptions. Without those 3 INTs the game would've been much closer and Oakland would only be down by 3 if they didn't go for the 2 point conversions after every TD. The offense of the Raiders was also kept Gruden's system, thus the Defense of the Bucs knew everything they were going to do.
And once again the Giants were beat by Baltimore's defense. The Baltimore offense scored 20 points, but the big story was that Kerry Collins threw 4 INTs, not letting the Giants' offense do anything, not even score. Without the defense, the game would have been much closer.
Even Indy's win last year is not surprising. They had the second best pass defense in the regular season and grew a run defense in the playoffs. Baltimore's defense stopped the Colts and the only points the Colts did score in that game was from the kicker.
While it is cliche, its a cliche for a reason, defense DOES win championships. The offense helps, but your "massacres" would not have happened without the defense.