Just watched ESO live, it was said that "on normal during the Tarcyn indrik fight, you will always fall on the same heighth and thus noe die, whereas on vet you will die on the 3rd fall".
I did MoS yesterday, normal difficulty, and I did experience higher and higher fall damage and died instantly form the 3rd fall. So it seems like this mechanic is present on normal difficulty, even if your dungeon designer said that it's only supposed to happen on vet.
PC-EU