Facts of Our Fathers?

I'm wondering where the notion popping up in coverage of "Flags of Our Fathers" that Iwo Jima was "the bloodiest single engagement the United States fought in World War II" is coming from.
Maybe it was up to that point of the war. But soon afterward, the invasion of Okinawa cost nearly twice as many American lives, more than six times as many Japanese military and an estimated 150,000 civilians'.
Was Okinawa, somehow, not considered a single engagement? Or, much as Eastwood's movie shows how facts were smudged about the Mt. Suribachi flag-raising for p.r. purposes, is there some promotional effort afoot to slightly obscure historical statistics in order to, utterly unnecessarily, make the film seem more dramatic or important?
Hopefully not. Truth may be the first casualty of war, as the old saying goes, but I'd hate to think that anything like that goes on in Hollywood.