Think about this:
Suppose a QB makes a throwing motion but never brings the ball back towards his body - he scrambles with the ball held out at arms length and then runs around like that for 30 seconds, and just before being hit he starts to tuck and before he tucks he is hit and drops the ball. By the rule it is not a fumble
Or consider that instead of staying behind the line of scrimmage he then starts upfield - still with the ball at arms length and never having been "tucked."
After he has gained 40 yards he sees he is about to be hit and starts to bring the ball in to his body and as he is doing so he is hit and drops the ball before it is "tucked" - by the rule it is an incomplete pass - is there a penalty for throwin the ball across the line of scrimmage?
What a stupid rule.