Family Man: If the sense of autopass is to speed up the game by allowing it to go on without having to wait for the opponent to make stupid "I pass" clicks, then it makes perfect sense that autopass is triggered when the dices you are going to roll don't give you any move.
Actually it would also make sense that "autopass" is triggered when you have only one legal move, since you will end up making this move anyway. This is what some people called "autoplay", and I have yet to understand why it was not implemented along with autopass.