I too think that probability there was several other culture shifts before the bombs dropped. It's just that the "50's world of tomorrow" was the dominate theme in the years upto the bombs. Tech most likely also had alot to do with being usable after EMP too hence all the anolog stuff. However it's mostly just because they never progress hardware past the vaccum tube stage but concentrated on other areas. They developed cold fusion for example, and with that breakthrough power armor. They you have energy weapons too thanks to cold fusion as well.
"Finishes his reports with a flourish" Finally! Anyway, I agree with my good person here with the Minigun, The World was stuck in the *50's world of Tomorrow* culture and technological wise, but developed things that would fit in the 50's norm. The cars looked exactly like you would see during the 50's with the high fins, huge bodies, and steel frames that take forever to rot away*especially in the rust belt*. Fashions were pretty much what you saw in propaganda films, dresses for the ladies, suits for the gents, unless it was a unique occasion that dresses were not practical. And Tech and buildings, besides what was mentioned above and what of it was left, had the 50's feel to it, like New Vegas, all the Major Casino's screamed 50's, and were like the old resort casinos of old like the Sands and such from LV.
In short there still is and pretty much a lot of the 50's still left in the Fallout Universe, even with the additions of more modern inventions that still retain some 50's style design to it. Please feel free to add anything else i might have missed people, I got to go get some food, these reports took me all day, and i got to go to the Mess.