While I understand the debate for LeBron as DPOY, I don't think people realize just how dominant Tyson was this year. The two games against Miami have been subpar for him as he's battling a flu.
Knicks were always a bad defensive team. Getting guys like Melo/JR/Novak/Baron/Amar'e wasn't going to help that. Other than Tyson, the only other good defender is Iman Shumpert. And to think, Tyson takes this group of bad individual defenders and transforms them into the 5th best defensive team this season? That's unheard of. Miami is just above the Knicks at 4th on the defensive rankings. At that point I would look at LeBron's supporting cast, which is FILLED with good/great defenders. Wade, Haslem, Chalmers, Battier, Joel Anthony are all very good defensively. Even guys like Mike Miller, Bosh, Turiaf are capable defenders, especially when they are inserted in the right lineup.
I think that's why Tyson won this award...because he basically single handedly transformed the Knicks from a mediocre/poor defensive team to an elite one.