From a development perspective, I think New Vegas is the one that stays true to the series while Fallout 3 goes against the grain, at least in this aspect of it. The world of Fallout 1 was of a working, functioning, developing society that only continued to improve in Fallout 2. Fallout 3 is the one where it still looks like the war just happened 200 years after the fact.
In lore terms, the New California Republic has created a functioning society of a large number of people (perhaps millions) on the West Coast while the East Coast lacks any kind of unifying civilizing force and is essentially in a state of anarchy.