Everyone on this board is watching an edited version of this movie!!
I suggest you run out and rent the film, if you can, to see the scene where Billy Joe admits that he willingly went with the man. It's too bad you are all commenting and drawing conclusions on a film that you haven't seen in it's entirety.
As to whether the movie is identical to the song, I would have to here the whole song in it's entirety as well. Anyway, the film is the film, the song, the song. Irrelevant at this point.
Also, I believe the film captured what Bobbie Gentry wanted to capture since...
"Gentry next surfaced on the big screen, credited as co-writer for a 1976 film adaptation of Ode to Billie Joe." AllMusic guide