It's all over but the shouting, I guess.
[Rango] has vastly outperformed [other animated features] in virtually every other respect [except box office]: critical reception (it is at 88% on Rotten Tomatoes, better than every other 2011 animated film except Arthur Christmas); early critics/precursor awards (it has been voted the year's best animated film by virtually every major awards-dispensing group -- among them the National Board of Review, Los Angeles Film Critics Association, Boston Society of Film Critics, and San Francisco Film Critics Circle -- except the New York Film Critics Circle, which skipped the category this year, and the New York Film Critics Online, which opted for Tintin); ...
My guess? The live-action directors Spielberg and Verbinski are the heavy-weight contenders for "Best Animated Feature" this year. They have the name recognition, the leverage, and the Big Mo.
Everybody else is in a lighter weight-class, doesn't matter how good the other pictures are, doesn't matter what the box office of this or that feature is. Heft and influence matter. That's the way Hollywood has rolled for the last ... oh ... century. It's the way the Academy of Motion Picture Arts and Sciences has behaved since it's inception. (With, of course, the occasional exception.)