Difōmā Raiton and going to zero Life Points
It's hard to say why Konami chose the specific replacement that they did, but the reason why the effect changed is quite simple: The effect would be inconsistent with the rules of the game.

Your third assumption is correct. Quite plainly stated in the rules, if any player's LP becomes 0, that player loses the Duel (or, if both players simultaneously reach 0 life points, the Duel ends in a draw).

When LP reaches 0, that's that - the player loses. As a real-world example, consider the second effect of the card Salamangreat Sanctuary:


  You can pay 1000 LP, then target 1 Link Monster you control; make its
  ATK 0, and if you do, gain LP equal to its original ATK. You can only
  use each effect of "Salamangreat Sanctuary" once per turn.


It is legal to pay 1000LP when you have exactly 1000LP remaining. In this instance, you pay the 1000 LP, your LP drops to 0... and you do not gain LP from the effect of Sanctuary. You will immediately lose the Duel at this point.



Now, just on the side: that's not to say that it's impossible to make the effect work for the physical card game. It could easily have been something like, "When damage would be inflicted to you that would reduce your LP to 0: Toss a coin and call it. If you call it right, your LP becomes 100 instead." But that's neither here nor there.