For me it is less about the possibilities for crits or fumbles, and more that the +1 WS is constant. I think it is telling that there is a skill (berserk charge) that grants +1 WS on the charge but there is nothing that grants extra attacks.
The combat system in 2nd ed is constructed where you try to build up the highest score you can, and you only get to generally use one of the dice that you rolled. So the main benefit of extra attacks is to try to boost the odds of getting a high roll. Once you have about 3 dice you don't really need more. A standard ork boy with 2 weapons rolls 3 dice. On the other hand, additional WS bonuses add to your total no matter what you roll or how many dice you roll.
I am really surprised that they did not simply make `Ere We Go grant Berserk Charge. But being separate rules they can stack.