It's a more serious incident than an injury as its as a result of a missile being hurled at 85+ mph! Concussion has become a serious issue in sport in general with teams/sportsman believing they can continue when they can't. This prevents teams taking undue risk with a player. I think it's a great initiative.
Though definitely ironic with the replacement getting smacked up early on! Even if England can't get the win, there will be serious fear in the Oz camp about Archer - reminiscent to Johnson in 13/14 down under. It's phenomenal stuff really.