I doubt that many people shoot with a dead vertical bow in traditional archery. Since we don't use bubble levels on our bows, it would be hard to maintain a dead vertical orientation. I remember when I first got into archery in the '80's, I started with a compound bow that I shot with a finger release. I didn't have a bubble level on my bow; they may not have even existed at that time, but I sure wanted one. I think I may have even tried to invent one myself, but I switched over to traditional archery before that idea got very far down the road, and never looked back.
Nor would it be really desirable to have a dead vertical bow, for the reasons Sam mentions above. We can cant our bows without the same negative effects on accuracy that would be the case with a compound bow because our bow hands are much closer to the arrow than with a compound bow. What we need instead of bubble levels and vertical bows is a reliable way to get the same bow orientation shot after shot. Fortunately, we have that if we have repeatable anchors and string blur. String blur can be your friend, although maybe not if it is in the exact center of your eye. I cant my bow a few degrees until the string blur is at the edge of my vision, which is almost like having another anchor. I try to get the same string blur in the same place every time I shoot the bow.