Fallout: New Vegas is based four years after the events of Fallout 3.
In Fallout 3 technology advanced rapidly, although society remained locked in the cultural norms of the 1950's, up until the nuclear bombs in 2077.
The Fallout 3 population is still living with the 1950's societal normality 200 years after this.
Despite the year now being 2281, in the Fallout universe, society doesn't seem to move all that fast for them, and the time era is still 1950's.
Even the convict outfit the "Kings" wear is based on the costume in the 1957 Elvis movie, Jailhouse Rock.
Not sure if you know, but Fallout was inspired by the 80s game 'Wasteland'. I've never played it though, I've only read about Wasteland on Wikipedia.
Watch what you read on Wikipedia, the free encyclopedia that anyone can edit. Find some strange things going on there sometimes, such as a picture of a rhino labeled as a duck.