Casino Royale was a modernized adaptation of the original book. It needed to be done in such a way to place it into today's world, but it still came from the book. Batman Begins is the origin story of Batman, which has been told several times before, therefore, it's still true to the comics. Gears of War is the story of Marcus Fenix's adventure to save mankind, not him going to prison.
And I know I'm being a little nitpicky about it because, even if they do make this movie, the sequel will HAVE to be the story of the game anyways. I'm just sick of seeing these big Hollywood execs taking a story and twisting it in such a way to make it their own.