New Vegas' world is superior IMO.
Well, seeing how I am replaying FO2 right now... there are a lot of blown out ruins in FO2. But, many are in random encounters.
The towns in FO2 don't look blown out, because... they are "new".
But, abandoned vaults, military bases, where people do not live, look blown out.
DC on the other hand, is not rebuilt, and the reasons are obvious. Feral ghouls, super mutants. Mutated creatures. Nobody lives in DC but ghouls.
Who is going to rebuild DC? Hmm lets go into a highly dangerous area and rebuild cuz it has been 200 years! Oh crunk I just got killed.
I would say most people who somehow lived, left the area, never to return.
Also, this assumption that DC going to be obliterated is nonsense. What is the goal of war? Kill as many as your enemy as possible. Hmm, California has 2nd largest city and 1/10th of the entire population. I'm surprised Vegas isn't ocean front property. Learn how to swim.
DC is worthy of a nuke or two. Seeing how the nukes, if fired from China, would hit west first, the idea of surprising politicians is pointless. So, your primary targets become highly populated areas and military bases. New York is a better target than DC.
For a tactical nuke, surprise attack scenario, DC is a prime target. For full fledged nuclear war where the system of govt, chaos, everything will be wiped out regardless, not so much.
Primary targets: LA, NYC, Cali, Texas, Chicago, key military targets and tech/industrial areas.