You might think so, but you'd be wrong. It's official canon that in the 50's, the Fallout universe branches off. In the FO universe, the culture stayed the same as in the 50's, and technology advanced much differently.
I think you need to look at Ausir's copy/paste another time.
The official canon says nothing more than that by 2077 the world came out looking like the 50's view of the World of Tomorrow. In the Fallout 3 manual, it says that the timeline split around 1950. There's nothing "official" about culture stagnating for 120 years. That's a rationalization tacked on by people to explain the end result. There's nothing in the lore to describe how we arrived at the end result in 2077, other than that's what it ended up looking like. It can be logically assumed that technology progressed in a different way - that much is obvious. But the actual cultural progression of the world in those intervening years is completely open (and largely irrelevant.)
There's two ways of looking at this - and both are rationalizations that the existing lore neither supports or denies. (Like Ausir said - if you watch an black and white sci-fi movie - everyone's still pretty much dressed the same and kind of looks like 1950 with neat gadgets. You see the same thing in 60's sci-fi, and all through to the present.) One rationalization is that society stagnated for 120 years. I think I've already explained twice in this thread why that's more outlandish a concept than anything else that occurs in the game. If there was some cataclysmic event that stopped cultural growth for over a century -
that's what the game should be focusing on, because surely that must have been a pretty interesting event to go against what has been a constant through all of recorded history.
The other rationalization is that society did indeed go through it's usual permutations. This doesn't mean that it had to have progressed in any way parallel to our own timeline. (For example, it doesn't mean that the hippie movement occured, or disco, etc...) It's nothing more than an assumption that culture went through it's usual cycles and that by 2077 it ended up looking like they always thought it would in 1950.
Again, both are rationalizations, and rather beyond the point. Neither is "official lore." I just happen to think one makes a whole lot more sense than the other. Fallout is a fictional world. The only important thing is the end result - the setting in which the game takes place. Which is in a destroyed World of Tomorrow. How it got there is largely irrelevant. It's kind of like discussing what the world of Star Wars looked like a few thousand years before the movies take place - the answer is simply "whatever was required to provide the end result." But if we were going to talk about that, I'd still maintain that literally the one thing you could be sure of was that Star Wars "pre-history" went through the typical cycles of cultural upheaval and revision that is a defining aspect of all cultures in the first place.