Most set ups will punch through a naked blade if you hit the wide flat part while it is hanging on a target. Many will smash through the spine part in the same conditions if tuned correctly - even low pound bows in the 45-50 range. Add hair, hide, meat and most critical - MOVEMENT of the critter and it is a different story.
We have all experienced the quick movement/reaction of a deer after a shot and this changes everything when you hit the shoulder. The parts that "move" the most are the muscles and bones in the shoulders. If you could get deer to stand statue still for every shot blowing through shoulder blades would be little issue.