The reason why is because your one character can switch to every class. So you go do your raid as warrior for two hours, then go switch the weapon for a healer one, then 2 hours switch it for a dps one... you get the drift. Other MMORPGS with that implemented do not have the ability for one character to be more than one class. Is it frustrating when you buy the wrong thing? Sure. Should we have the refund option? Heck no, that can be so abused with the mechanics in this game.