Someone said this at TFN...my first thought was 'typical defensive gusher stuff' , but now I think the guy may have had a point:

The Dark Knight is a sort of prestige title for Warner. It could almost be like another Titanic. Its going to dethrone Star Wars before the month's over and if they push it enough it could come within striking distance of Titanic. The whole "box office race" is seen as a significant competition, to be able to catch Titanic--no ones ever come this close.

Anyway, Warner probably wants Dark Knight to go as far as they can take it, even at the expense of other films of their own. If they have $20 million in advertising this month, they might still take 50% of that for Dark Knight, even if its a month old, and sacrifice some of their new films.

Well, Warner is also distributing Clone Wars. For a Star Wars film it really hasn't had a huge publicity push. You see the odd subway poster and the odd commercial. But less than what is typical--the vast majority of the buzz is from LFL itself and from fans. And right now analysts are predicting late teens for the B.O.--I think thats an underestimation, I think it'll do early 20's because of the grown-up audience that will come opening night and give it a bit of a kick.

But given the terrible word of mouth--this is one of the only times in recent history that a studio has actually enforced a review embargo, even after they invited critics to the early screening--they are probably just letting Clone War slip out there, make more than its meagre $10 million (or so) budget, and then disappear.

In other words they don't want it to dethrone Dark Knight. It would look good if Dark Knight stayed number one again--and it would look very bad if Clone Wars was the title that finally took it down. I think they might honestly want the film to underperform.