OP has a valid point, though:
Blizzard is going for a healing model where mana matters. While this is the intended game style I also don't like it at all.
Healing should be limited by skills and cooldowns just as dps is. The whole mana thing is a giant annoyance. I'd much rather have an energy based healer or a healing system where mana functions more like energy does right now than the current system. I hate mana.
But since Blizzard does not share that opinion I guess we are stuck with mana being super important and that's not going to change any time soon.