Ben Stiller’s “Tropic Thunder” was the #1 movie for the third straight weekend, which is actually quite impressive given the way distribution works these days.

(Remember how “Indiana Jones and the Last Wheeze of the Franchise” was dethroned after one week by the “Sex and the City” movie? I bet Steven Spielberg does.)

But nobody’s paying attention to that. The story of the weekend is “The Dark Knight” breaking $500 million domestically — it’s only the second movie to do so, after “Titanic”.

That iis, indeed, something to talk about; grossing half a billion dollars in less than two months is unprecedented, and the bigness of the number is an elegant way to step around the generally meager returns of Labor Day weekend.

Still, “Tropic Thunder” hanging on to the #1 postion shouldn’t be completely ignored. It’s one more jewel in Robert Downey, Jr.’s crown … between this and “Iron Man”, he’s given Paramount’s summer a far larger boost than either Harrison Ford or Mike Myers. And who would have seen that coming this time last year?