New Jersey is in a weird situation. For them, it's more profitable to sell tickets at a higher price. The owners aren't too worried about attendance figures. I recall that New Jersey is, indeed, doing well in that regard, unlike some teams in the Southern US. Not sure how general revenue is fitting in here (concessions, parking, merchandise...etc.)
Approach to exaplain the attendance situation for the Devils is the NHL team density in the region. They are three "older" teams in the region (Rangers, Flyers, Islanders.) New Jersey State was divided between both the Flyers and the Rangers, before 1982. Being in a tough market and starting off slowly after relocating over from Colorado adds to the troubles.
The evolution of Devils fans is a slow one, because the long-time Flyers or Rangers fans, for example, have a tendency to pass their love for their club from generation to generation.
That's how I understand the situation in New Jersey. Feel free to add or to correct my points!