Although the New York Giants beat the New England Patriots 21-17 in Super Bowl XLVI, they weren't the best team in the 2011 NFL season. On there way to winning the Lombardi Trophy, the Giants were the hottest team towards the end of the regular season and into the playoffs.
This is not to say the Giants are undeserving of their Super Bowl victory, but actually the opposite. It makes their Super Bowl run and championship even more impressive that throughout the year, they weren't even in the top five of the NFL's elite.
The NFL has changed significantly. Where it was once about being the best team all year long, it has now become all about clicking at the right time and carrying that momentum into the playoffs. The Giants perfected that this season on their way to Super Bowl XLVI.