Can someone explain the reasoning behind the game ending with 1 second left on the slow motion replay clock.

I heard something about there has to be 2 seconds for replay to put time back on the clock. My guess is the reaction time of the ref seeing the ball hit the ground and signaling incomplete is 1 second. So when the ball, in slow motion, hit the ground with 1 second remaining, is allowed to run down to 0. Anybody have the actual reasoning?
The rule doesn't make sense and should be changed. Even though the replay clearly showed a second on the clock when the ball hit the turf, there is no provision made to determine when the whistle actually blew the play dead. As a result, the rule states that when the call on the field happens within 2 seconds of having the time expire, it (the call in question) is not open for a review. Yes, the ref may have sounded his whistle immediately upon seeing the ball hit the turf, but maybe not. Since the clock operator starts & stops the clock based solely on the sound of the whistle, it is impossible to know if he (the clock operator) should have allowed the time to expire or not.

Obviously in this instance it worked to our favor, but it would have been hard to see that happen if we were on the other side of that call. While I understand the reason for the rule, I can also understand how the video evidence alone should be enough to know that one more play should have been allowed. Rules are rules even if they are dumb.