I still think it's likelier flamestrike is up for the cut than the abilities being spec-locked. Arcane Explosion and Blizzard form two aoe niches for the Mage class, one spammable and mobile up close, the other channeled at range with a cc component.
Both abilities have been available to mages since the earliest days and most importantly, both work. Flamestrike is the clunky red-headed stepchild with it's long cooldown and cast time.
Spec identity and flavor is important, I agree, but we aren't going to improve it by limiting each class to a single aoe spell in each spec that may not be as good for a given situation as another.