This is a poor explanation. All SE could have done is a flat damage reduction instead of reducing the effective attribute state, which they should have in the first place.

The real reason dmg is no longer affected by vit is because SE desired to make the game harder, and it's been a long standing fact that DPS helps tanks maintain aggro. The result of this is, no one really needing to take care of their own enmity, and therefor tanks like warriors were running entire dungeons in DPS stance. They wanted them to use the class as intended.