For starters, a scoped rifle can well be shot with both eyes open for the same reasons given for shooting a bow with both eyes open.
I shoot tradbows with one eye closed, my left. I am right eye dominant, and shoot right handed. I instinctively gap-shoot. It has helped me focus, and tightened my shooting. Long before I ever tried it, I'd heard, understood, believed and repeated the conventional wisdom of keeping both eyes open. However, if there's one thing that MBB DVDs taught me, it is that many are the paths to shooting happiness! We're all different, and what works for one may not work for another. I shoot with my left eye closed only at normal bowhunting ranges. When I have to raise my arrow tip above the target for a longer shot, I open both eyes so that I can see the target, otherwise it's obscured.