I (unfortunately) game online with a couple guys from Pittsburgh and they both have the same opinion, as do a lot of fans on other forums that i've followed this season. Kessel has been the better player, better on the PP, and taken a lot less stupid penalties that have led to goals against. Crosby already has 40 PIM this season and has been struggling to stay disciplined at key points of the game.
On top of that, Kessel has a career of being snubbed for whatever reason even though he's consistently great year after year. He's on a team with Malkin, Crosby, and Letang, and is outscoring all of them and still can't get a nod for what he's put together.
Plus, he's an American hero.