Other than the developers comments, where is this written or stated? Or is it just common canon? I mean, a childrens Toy from the 50s or pictures without a context are not really saying that people in the 50s imagined a dystopian postnuclear World of Tomorrow = the Fallout Universe.
Honestly, I don't remember anything being specifically explained in the Fallout 1 or 2 game manuals. Back then, I think we just kind of put two and two together. :shrug:
I mean, you take the retro-sounding opening song, all the vacuum tubes and other retro trappings, and then combine that with more futuristic things like Plasma Rifles and Power Armor, and the rough timeline you were given - and it just kind of coalesced eventually, as I remember it. To my recollection (and memories can be wrong, of course) it was a more intuitive connection than anything else. You just kind of accepted it and moved on.
Personally, I don't think it's the sort of thing where you're really supposed to over-think it, either. All this talk of "divergence" and such - I don't think the game was necessarily designed, originally, with much more thought than "how do we intuitively drive home the concept of an idealized future world that was then obliterated in a nuclear holocaust?" (Though, obviously, not being a developer on the original games, I could very well be entirely wrong.) Going into "why did culture remain stagnant for 120 years," or "what cultural revolutions and divergences led to society coming full-circle in 2077 and appearing as an idealized version of 1950's futurism" is kind of missing the point, I feel.
(My thoughts, anyway :shrug:)