Originally Posted by
Endus
Every spec has several factors they are supposed to be monitoring to maximize their performance. For the most part, mana isn't one of them for caster DPS. Caster DPS are designed with multiple cooldowns and DoTs and such to monitor, and interweaving those properly is what defines and limits their DPS. Melee typically have a resource system that is central to what limits their gameplay flow; Enhancement is a notable exception, in that it has a more "caster-y" focus on cooldowns rather than a resource limitation. Healers also, in theory, are watching mana consumption, though this has become less of an issue as time goes on in both Cata and WotLK.
The only reason casters should have to watch their mana is if melee DPS would have to watch their own resource levels. And by that, I mean they would have to be actively using abilities to generate more Rage/Energy/Runic/etc, abilities that do crap or no damage, because not using them leaves them "oom". Their resource generation isn't restricted by ability use, and neither is a caster's.