The Saints scoring on the two-point conversion was indeed a blown call.
Does that "devalue" the Saints winning the Super Bowl? No, but it was still a pretty big blown call. The radio announcers for Westwood One were particularly upset with how the refs overturned the call on the field of an incomplete pass, which it was. Lance Moore did not have complete possession of the football as it crossed the goal line plane when the Saints were trying to take a 24-17 lead. A ref was right there, watching the catch, two feet away and made the correct call. Replay over-turned it, but the explanation for the over-turned call was very poor.
Here's the official explanation from outgoing NFL V.P. of officiating Mike Pereira (via NFL spokesman Greg Aiello): "By rule, when a receiver with possession of the ball is in the act of going to the ground and performs a second act by reaching out to break the plane, that completes the process of the catch and the ball is dead when it breaks the plane."
But that's not what the rule says. Here's the operative language: "If a player goes to the ground in the act of catching a pass (with or without contact by an opponent), he must maintain control of the ball after he touches the ground, whether in the field of play or the end zone. If he loses control of the ball, and the ball touches the ground before he regains control, the pass is incomplete. If he regains control prior to the ball touching the ground, the pass is complete."
Basically, Pereira is applying an interpretation based on the assumption that Moore, while falling, secured possession and pushed the ball deeper across the goal line, before losing possession.
Again, that's not what the rule says. It says that if the player is going to the ground in the act of catching a pass, he must maintain control after he touches the ground. Not during, but after. In other words, he must keep the ball until he comes to rest.
In the end, it was not a major play that necessarily decided the outcome. It's just another example of how all the breaks went the Saints way.