Just as this year’s Oscar race began to look settled — with “Avatar,” James Cameron, Jeff Bridges, Sandra Bullock, Christoph Waltz, and Mo’Nique winning virtually everything — the Producers Guild of America dropped a bombshell onto our illusions by presenting its Darryl F. Zanuck Producer of the Year Award not to the box-office bonanza “Avatar” (20th Century Fox, 12/18, trailer) but rather to the critics’ darling “The Hurt Locker” (Summit, 6/26, trailer).

That’s right, producers, that rare breed of money-hungry urchins, liked the movie that’s made a mere $16 million so much that they gave it their prize over the one that’s made $1.8 billion (on the very day that it surpassed “Titanic” to become the highest-grossing movie of all-time). In case you need it spelled out for you, that’s an upset of epic proportions — the cinematic equivalent of David slaying Goliath.

Anyone who tells you they saw this coming is a liar. Most of the people who follow this stuff closer than anyone — the top Oscar bloggers — actually did other things tonight rather than sit around waiting for the inevitable “Avatar” win that never came. (My former colleague Sasha Stone of Awards Daily actually called off her annual PGA prediction contest, writing, “Everyone knows that the PGA will go for Avatar.”)

So how did this happen? Some will suggest that a contingent of the guild didn’t want/wasn’t ready to embrace a movie with as much CGI-use as “Avatar”; or that votes basically split between “Avatar” and “Up in the Air” (Paramount, 12/4, trailer), thereby allowing a third movie to prevail with fewer votes than usual; or that “Avatar” is simply not as popular within the industry as it is outside of it. There may be a degree of truth to all of these theories, but I believe the real answer is this…

At the end of the day, voters tend to vote for who/what they like, not who/what they’re “supposed” to like. That’s why the Academy didn’t nominate “The Dark Knight” for best picture. That’s why “Crash” beat “Brokeback Mountain” to win best picture. That’s why Adrien Brody upset Jack Nicholson and Daniel Day-Lewis, and why Marion Cotillard beat Julie Christie and Ellen Page, and why Alan Arkin beat Eddie Murphy. And that’s why Bullock has already won so many awards this year — and may yet win the Oscar — for “The Blind Side.”

I can’t even begin to tell you how many Academy members have told me, “I prefer ‘The Hurt Locker,’ but I think it will be ‘Avatar.’” They may be right, or they may not be. What could well prove to be the case, though, is that this group accounts for a silent majority — people who, while privately filling out their ballots, will vote not the way they think they’re supposed to, but the way they want to, precursors and box-office be damned.

Perhaps we should be asking some harder questions about “Avatar,” too. We know that a movie can win the best picture Oscar without an acting nomination — it’s not easy, but “Slumdog Millionaire” did it just last year — but we don’t know if it can do it without the unreserved backing of actors, who represent the largest percentage of the Academy’s membership. “Slumdog” did win the SAG Award for best ensemble, whereas “Avatar” wasn’t even nominated, largely because many actors fear that films like “Avatar,” which feature digitally manufactured and/or perfected characters, will lead to a future in which human actors will be much less vital to the filmmaking process. (Mark Harris has a terrific piece about this very issue in this week’s Entertainment Weekly.)

What I do know is this: Exactly a week ago, I stood before Cameron in the press room at the Golden Globes, where he had won two prizes within the previous half-hour, and asked him if it was fair to say that he was again “the King of the World” again. While some people chuckled at the memory of his previous Oscar night faux-pas, nobody — least of all Cameron — laughed at the underlying premise of the question because it seemed so certain that he and “Avatar” were well on their way to repeating what he and “Titanic” did 12 years earlier: steamrolled to a bunch of Oscars on the back of critical and commercial success. Thanks, however, to tonight’s PGA shocker, Cameron and his ex-wife appear to have on their hands a serious battle for custody of not only the best director Oscar but the best picture Oscar, too.

For a sense of what a best picture victory for “The Hurt Locker” might look like, check out the video below, which was captured backstage at the Gotham Awards on November 30, moments after the film won that award there…

Photo: Jeremy Renner in “The Hurt Locker.” Credit: Summit.

Video: The team behind “The Hurt Locker” celebrate its best picture win at the Gotham Independent Film Awards. Credit: Rob Perri (video), Dr. Harvey Kliman (post-production).