You know, it used to be a singular shell back in Beta I believe, but every one complained because it messed stuff up. Too potent, which is why they reward preparation and micro with shell use. Annoying at times, yes, but ultimately rewarding once you pull off a good infantry wipe, or dank tank hit.
Beta? It was one-shell-type even year ago I belive. Well, point is it was in game (not just in beta) for a long long time.