In one of the interviews with todd howard in Utah he mentioned that when dragond breath fire its them doing a dragon shout, and then he was questioned on if the player could then do it as we have access to dragon shouts, to which he replied yes. personally i think this is awesome, i can imagine a dragon breathing fire on me and me just breathing it right back at him. also it means that we can have a magic fire attack even if both hands are occupied by weapons or a shield.