People use terms in this game however they want, whether they're right or not. I tend to agree with you, I never had anyone in WoW say something like "they're both my main spec". Main spec typically referred to what loot you would roll on with DKP, if you were REQUIRED to heal to make the fight happen you wouldn't be punished by not being allowed to roll on main spec gear. It was the class you wanted to gear faster. That doesn't necessarily apply to this game because of the loot restrictions though I guess.