Because in some Dungeons the Mobs dispel like hell.
But here we come to some more interesting PRCs like the Dweomerkeeper (or Dweomercheater like my players called it) *** his ability to make a Supernatural ability out of some spells.
Supernatural Persistant Divine Power or "Why are Clerics the better Fighters"
I even remember some cheesy stuff with a Mystra cleric who could cast inside a Antimagic Field.
Divine Metamagic was one of the ey reasons for the incredible powerful Clerics ind 3.5 (even if they got hit pretty hard by the Nerf Hammer after 3.0)
But im not entirely sure how that would work out here in DDO since you cast FAR more spells per rest then in DnD.
But from the principle, the cleric needs a buff, yes