in self-defense, striking attacks can come like a drunken man's flailing, unfocused punches or mike tyson's cannonball straight punches. (just example, boxing fans please don't pounce)
both of them can hurt if we're not prepared for it.
IF our training has any self-defense purpose within ( however small ), then stylized attacks where ukes CAN be wrong is a big mistake.
however, to create order and proper training atmosphere in the dojo, an uke is expected to do what an uke should; attacking with a focus, and do ukemi afterward. I think too much of this can ill prepare practitioners of this art in real life.
but training 100% self-defense aikido isn't good either, so I try to do everything in moderation. Changing focus every once in a while.