And who won the superbowl that year? That's ridiculous takeaways are probably the most important stat for any team.
The defense was built to gamble and force turnovers because even if they gave up the big play, they knew they would go right back and score. The Saints won the Super Bowl mostly because of their prolific offense (and cheating - coming from a Vikings fan), not solely because they lead the league in turnovers and defensive TD's.
Defensive TD's are often quite random in nature. In 2009, Darren Sharper seemed to always go for a pick six. The next year, I believe the Saints struggled to keep up the turnovers. A lot of the random luck that helped in 2009 did not go their way in 2010.