I think a lot of confusion is getting kicked up because of the razerdon not having to take -'s for so many of their ballistic conditions
Yeah then you could say the same for anything mounted including cavalry, chariots and characters on monstrous mounts. If the base moves, the model counts as moving, though war machines may turn on the spot without penalty.
A lumbering stegadon isn't exactly the most stable platform from which to shoot. I imagine we're lucky to only get a -1 penalty!