true, but it still centered around vaults...
So? Then center it around vaults. For instance, create a storyline of a vault dweller from vault 112 set in , I don't know, the year 2234, when it was still closed or something. Or go the Fallout 2 way: the protagonist from Fallout 3 has an ancestor living in a town around washington DC. There are still lots of possibilities. And since
Spoiler Vault 101 was supposed to be closed for eternity but apparently your father was able to get in right after your birth
storywise there shouldn't be much trouble. Besides, who says they can't develop a story about a Vault that was opened and used it's GECK to create a city. I'm visualising it right now: "It is home. Your home."