ORIGINAL: Lebatron
Part of the strategy of passing when your opponent does is to advance the round. If you are the defender and have to hold something for 5 rounds to win and your opponent passes for some reason you should make him pay the price. When I first played the board game against a stronger player I made this mistake a few times. So in fact it is critical to know when your opponent passes.
I don't have any experience with the boardgame, but I think I will disagree with your disagree (we can agree to disagree too [:)])! My reason is this, you would still see the message that the opponent took some unknown action. You know your opponent either performed an action out of your LOS, or passed. In your scenario above, the defender could take a gamble and pass too, hoping that the opponent did to move to the next round. So there is still the strategy, but you must also take a risk since you don't know for sure.
Now I understand this wouldn't be 100% true to the board game, but in my opinion this makes for a better computer game, taking advantage of the features that could be offered on the computer. I would also be more than happy if this behavior could be added as an option so each player could play in their preferred manner so we both could be happy. [:)]