Why is that I wonder? It really does make you think; The 1950's era feel was difficult to "get a feel of in the first games". Its almost like the architects of the series got it wrong...
At least it seems so until you consider that the game was set in an idealized 50's future paradise that met with a harsh dose of 'real world' desperation and unexpected demise.

Fallout has no greasers and beehive helmet haired wives, or bubblegum chewing clicks of school girls in poodle skirts ~Fallout is set in 2161. For 80 years folks either lived cushy in the vaults or suffered hell on the surface. Everything 50's-esque in Fallout came from before the war (and most of its broken). Its the architecture (the little of it still standing), and the rusting heaps of old vehicles There is very little anything resembling 1950 in the world that the Vault Dweller emerges into (even if though that may have been what he expected ~or not... Its never really pressed or made definite as far as I ever saw). The closest thing to 1950 anything that I can recall in Fallout is Decker himself and Butch ~and that's it. :shrug: (maybe Gizmo but its a stretch). Its a brave new world where the mutations resemble the 50's SCI-Fi monsters; and radiation really makes green ghouls ~The Fallout world's physical laws are in sync with the pre-war hysterical beliefs about radiation and atomic bombs. While there is no denying the retro-futurism of the series; there is nothing in FO1 that implies that the present day world there is "stuck in the 50's" (it just has common aesthetics ~and always will... even when designing computerized fusion powered robotic infantry armor for a nuclear ground war). Take the above as my opinion only; having played the game.

There is a long standing pattern in this series. First Fallout 1 set the stage; then Fallout 2 expanded it, and IMO (have to say that), started straying from the design with things like the chess playing scorpion, and mobster suit wearing gangsters toting tommy guns in the year 2241. Tactics left the whole RPG part behind entirely, and FoBOS.... well... yeah.
Come Fallout 3, we find a hodgepodge mix of rehashed aspects from Fallout 1 & 2, with a heavy bent on a 1950's mania in present day people... Like the Tunnel Snakes (all dressed up like http://www.shanana.com/). IMO its gross misinterpretation of the material. Sometimes right, sometimes not ~sometimes waaay off the mark.

But it didn't play a huge part in the games before. Nuka~Cola was an awesome joke because it was addictive. (Same kind of joke is done again in FO2's film studio, where you hire on for a job in New Reno and immediately get poisoned.)

How?
*Not to mention that supposedly all ~ALL~ ghouls come from Vault 12; though its at least plausible that east coast ghouls could result from similar circumstance. I don't see the purpose for getting a better feel for the Ghoul's lifestyle since the PC can't ever become one (and Moira and any others that did ~shouldn't have). I did like the Ten Penny Ghoul ending until I realized that it changes nothing, and Ghoul merchants pop out of the ether to begin selling there.
Towns in FO were acceptable; towns in FO3 were http://www.merriam-webster.com/dictionary/incredible.

200 years later, you can find mini-nukes in old barns and unlooted first-aid kits that have advanced military drugs designed for the battlefiled. I'm not disputing what you are saying, but none of it made any sense IMO. (Which is part of the mistake... Fallout was not about wacky absurdities ~unless you were in the deepest wasteland, and its an in-joke for the player ~not to be taken completely literal... It is and it isn't).
One of the things that actually impressed me about Fallout was that most of the drawers and lockers were actually empty unless you were someplace that no one had been for looong time, or were in someone's building that they used frequently.