Probably because Arcane Warriors are mages that focus on melee combat and so don't use as many spells. In the computer game they didn't have access to any unique spells at all, just specialisation abilities which focused on defence and combat.
DracoDruid wrote:Hmm... but they don't get the spell automatically, right?
I dont believe they get it automatically. Not realy as they could focus on other spells rather than the Aura, with their selections, it is just giving them an option to gain a different spell without actually giving them more spells they know.