Interesting. If true, the film is misleading.
It has been a while since I read the book, but Iwo Jima was the last outlying bastion the Japanese had before the "Home Islands" and it was very important that they hold it. It is spelled out by James Bradley, but I can't remember the details. I do remember the details of what the Japanese did to the poor American Medic they caprured and tortured for 3 days. Sickening, to say the least.