From my perspective, the vote shouldn't have been close.
All the respect in the world to Clay Matthews, but Troy Polamalu was the unquestioned Defensive Player of the Year for the 2010 season. As we saw both last year and this year, without Troy Polamalu, the Pittsburgh Steelers are not even a playoff team, let alone a Super Bowl team. They're 9-8 in two seasons with him out of the line-up.
I have no idea why eight people voted for Steelers linebacker James Harrison. He pretty clearly is less 'valuable' to the Pittsburgh than Polamalu, who received 17 votes. Clay Matthews, who the Colts came this close to drafting in 2009 (picked one spot ahead of Donald Brown in the first round), received 15 votes.
Polamalu is only the fifth safety to ever win this award. Other safeties include Dick Anderson of the 'no-name defense' Dolphins in 1973, Kenny Easley of the 1984 Seahawks, Ed Reed of the 2004 Ravens, and Bob Sanders of the 2007 Colts.
Anderson is the only safety to win a DPOY award the same season his team won the Super Bowl.
While we all appreciate Bob Sanders' contributions from 2004-2007, it's pretty obvious at this point that Polamalu is a far superior player. And when people look back on the 2000s and think of great safety play, Polamalu and Reed will be the standard while Sanders will be a footnote.
Such is the NFL.