I think JZarr hit the nail on the head with his explanation. I also saw that demonstration in a video where the rubber tubing (simulating arteries) were pushed aside when a dull blade passed between them, thereby causing less trauma upon pass through. Then they pushed a razor sharp blade through and every strand the blade touched was severed to allow for faster bleeding and a more humane kill.

No doubt that a double lung hit with a slightly dulled blade would bring the animal down, but as you said, " if penetration was an issue then the sharper the head the better because the blades would not drag as much." Isn' t penetration always an issue since we cannot possibly tell exactly what we' ll hit (bone, shoulder, etc.) until after the shot is over? So, if the blade strikes shoulder or rib bone and doesn' t have the sharpness needed for the required penetration, the arrow may only strike one lung and end up in a tedious day of tracking, or unfortunately lost game.

We all owe it to the game we hunt to use nothing but the sharpest blade possible for a quick, clean kill.