In looking at the Pittsburgh Steelers / Arizona Cardinals match-up, you have one team that traditionally plays a solid defensive game against one that can put lots of points on the board in a hurry. In baseball, good pitching can cancel good hitting. In football, though, it isn't quite as simple. All you need is on defensive back, for example, to look over the wrong shoulder and the result is seven points. Or the defensive call could be an all-out blitz, which is picked up and a slant pass ends up going for a long score. Conversely, you could have the good offensive team with a few scores, but some defensive adjustments and the resulting turnovers put the team with the good offense in the hole, and when the entire stadium knows a pass is coming, the defense locksdown.
In other words, stop looking at the vaunted Steelers against the high-flying Cardinals. A better view of the game might come from reviewing the Steelers offense against the Cardinals defense.
In short, the Cardinals give up almost as many yards as they produce, while the Steelers have had some offensive struggles. Arizona had some ugly losses this season, giving up 56 points to the Jets in September, 48 points to the Eagles on Thanksgiving night and giving up 47 points to New England and 35 points at home against the Vikings on back to back weekends in December. The Steelers did score over 30 points in four different regular season games and once in the playoffs.
Although when handicapping football games, I hate Hate HATE hearing about emotional stuff like "The revenge factor", or that "they want to win it in front of their fans". Trust me, in the middle of the third quarter of a close game, the QB is not in the huddle saying "Two years ago this team beat us and knocked us out of the playoffs, therefore we want our revenge and will win." Instead, he is probably saying something like "Right 46 Fox, Left Swing Swing Mike 11 on 2". This entire paragraph is completely irrelevant, however, as neither team really has an emotional advantage or disadvantage. I was just seeing if you were paying attention.
The bottom line is that the Pittsburgh offense is better than the Cardinals defense. Arizona has been very hot in the playoffs, but in reality they are a 9-7 team that won their division by default. They have no discernable running game, their star receiver pouted at the end of the Championship winning game, and their quarterback - though a good story - is old with a history of being a fumbler. Take Pittsburgh straight up.
If you are playing against the spread (Pittsburgh -7), it gets a little tougher. If the Steelers are ahead by two scores late in the game, their defense may back off a little and Kurt Warner could pick apart the prevent defense for the backdoor cover. But I don't think that will happen. I actually think that Pittsburgh's good offense against the Cardinals suspect defense will allow the Steelers to take a nice lead into halftime, and as the game progresses and Arizona's offense presses, the game will get out of hand. Take Pittsburgh laying the TD.
And for your bonus prediction of 46.5 over/under, for the reasons in the above paragraph, I think Pittsburgh will light up the scoreboard, and Arizona might through in a garbage TD, too. Also, the score went over in 13 of Arizona's 19 games, and in 10 of Pittsburgh's 19 games. Take the OVER.