Healing in P&P is also gated by the number of spells that divines can cast, which forces a party to deal with issues such as strategy, damage mitigation and combat tactics.
Much of this would also be the case in DDO if casters really were limited by their blue bars. The availability of SP potions throws the game entirely out of whack and makes it impossible to achieve any sort of game balance. There's no possible way to make a raid that is challenging and fun for a group that uses none of such potions, and isn't a complete pushover for a group that uses 50 of them. Even with different difficulty levels.
Even a timer on these pots would help, as you suggested. But it won't happen. Much as people complain about "pay to win" over stuff like tomes, those little blue vials are actually the worst offenders, and Turbine simply makes too much money on them to hinder their use.
SP pots are DDO's equivalent of "the spice must flow".