The law is clear:
10.4 (e) A player must not tackle an opponent whose feet are off the ground.
The law is an ass? Yes, when applied to a player running with the ball. No, when protecting a player jumping to catch a kick.
Should it be applied to a player leaping to catch a ball thrown above his head? It would be easy to say "Yes! We must protect vulnerable players" but, as Ian has shown in graphic detail, the application would be impractical.
As to the tackle in question: Correct in law, wrong in application. The fact of no citing is significant.
I agree with parts of your post but not the part I have made bold. Are you talking about Ian's car accident example or his analysis of reaction times?
As the Laws stand at the moment, it is the tackler's responsibility to execute a tackle legally. This includes not tackling a player without the ball and not tackling a player who is in the air etc.
The fact of the matter is that the AB player tackled a player in the air and was penalised. Therefore, although it may not have been a popular decision, or in fact one that many grassroots refs may have let go, it was a correct decision in Law and as such cannot be viewed as a critical Law error as argued by Pegleg.
A tackler tackles an opponent on spec, believing that he was going to receive the ball but didn't = the tackler takes the risk
A tackler tackles an opponent, who has jumped to catch a ball, before he lands = the tackler takes the risk
A tackler lifts an opponent and turns the player past the horizontal = the tackler takes the risk