There are two lines of NFL conventional wisdom that do not work.
First, the Brett Favre signing by the Vikings has raised the team to an NFC favorite, Vegas put the odds of the Vikes winning the NFC at 6-1, down from 12-1. Brett Favre has not made the Vikes the best team in the NFC, and the Vikings will not be the conference champs for the first time since Super Bowl XI.
Here's the argument: Favre will have a great running game, and a great defense against the run, and the team only needed a new QB to become a champion.
But that combination of great running game and defense sounds just like the 2007 Steelers (3rd in rush offense, 1st in total defense), who had a QB who threw for 32 TDs with just 11 INT, had a 1300-yard runner, and lost at home in the first round of the playoffs, just like the Vikes did last year. And it sounds like the 2008 Jets, who had a top 10 running offense and a top 10 defense against the run . . . and went 9-7 and watched every playoff game.
The Vikings barely beat the Giants in the final game of the season last year. The Vikes needed to win to make the playoffs, the Giants rested their starters (no Jacobs at all, Eli sat the second half, various lower workloads for the starters on defense and offense). And the best run defense in football (Minnesota) allowed 135 yards on 30 carries to the Giants' #2 and #3 runners and won only because the Jints had missed a field goal earlier in the game. With nothing to play for, the Giants acted as if the game were a preseason matchup, and nearly won.
Minnesota just was not that good last year: the Vikes should have lost to Detroit at home and won by just four in Detroit against the worst team in the past 30 years. They were no match for the Eagles or Titans. The Jets' improvement from 2007-2008 came as much from having a healthy QB as having a healthy QB named Favre -- look at how well the Dolphins did with the 2007 Jets' QB as their signal-caller (unlike Favre, Chad Pennington has never started 75%+ of his team's games and NOT made the playoffs). The Favre factor may enable another win for the Vikes, but they're not in the top three of the conference.
The second strain of conventional wisdom is that the Giants need a #1 receiver to win the Super Bowl. That's rot. The Giants' defense wilted in the last quarter of the season last year because the team lacked defensive end depth. The Giants' offense failed against the Eagles, twice, as much through error and game-planning (Domenik Hixon's dropped TD in the regular season, Coughlin's bad wind decisions in the playoffs) as the absence of a #1 receiver. The Giants lost to the Cowpatties in Dallas because the Cowmanures were desperate for a win (the Giants knew the next weekend's game against Carolina would be for the NFC's #1 seed), and the Giants didn't have Jacobs available. The Burress mess occurred at the worst possible time because the Giants could not reconfigure their offensive game plan against the Eagles as quickly as the Eagles revamped their defense against the Giants. But the fact is that the Giants had two of their best passing days with Burress out of the lineup (against Seattle and at Washington).
The defense was spent at the end of 2008. The team blitzed on 40 of Philly's 46 passing plays in the playoff matchup but only had one sack and few hurries. The Giants had five sacks in games 12-17 of their season. They allowed 28 points to the Panthers, had the Panthers run all over them and won only because Derek Ward went off. Tom Brady won three Super Bowls without a top-end #1 receiver, so did Ben Roethlisberger, so did the Bucs under Gruden. If the defense is healthy and rested, the Giants can go far.