With a game like Fallout the gameplay mechanics are at least as important like the setting and the choice of narrative. It's the sum of the parts.
And as we know... The setting for Fallout was arbitrarily decided later; the gameplay was the focus, and the combat system came first [afaik].
I would be very,
very, surprised to hear that combat was the very first thought about fallout. It seems very clear to me, that besides alpha build, the first focus as far as design philosophy, was the pen and paper mechanics. As in, multiple endings for every quest, the world changes around you due to the choices you have made. Heck, there are people that WILL not talk to you anymore if you piss them off, and you can just suck it as far as the quest goes. Nevermind starting a fight, and so and so, just happened to get winged, jump in, die, and now that quest is gone forever. That's a fuck of a lot more believable then, no matter wheat choice I make, it doesn't matter, because it basically works out the same. Except of course the megaton quest that results in you getting a house, or possibly getting a house. And that is one of the most choice focused quests in the game......
