Shag, with Geoff Johns as the writer on Justice League as well as CCO, I think that adapting the New 52 Justice League into a movie was the point from the very beginning.
I mean, who are the first three heroes we meet in costume in the Justice League story? Batman, Green Lantern, Superman. Not a coincidence. And we get to see a little bit of Victor "You'll be a Breakout Character If I Have to Mindwipe Every Reader!" Stone as a civilian just like you would in a film.
The entire thing is synergistic. Go see the movie then DC can sell you a trade or HC of JL #1-6 which is the same story. Oh and then you can buy volumes2 and 3 which continue the story! *winkwinknudgenudge*
I've only read the first issue so I am not in a place to judge. But it's logical if nothing else.