First, this still doesn't address what Ghoul's were up to for 200 years. Second, the potential for "effects" to last centuries doesn't say much. What level of nuclear war must have occurred for these long term effects to exist? What exactly are these effects? How are we determining the scope of their impact? How much of an effect do they still have after ten years? After 50? After 100? If DC was hit so hard as to prevent any rebuilding for nearly two centuries, then why are there any buildings still standing, especially those in the heart of the city?
Radiation is the effect, fallout. It isn't all "BOOM", the menace of nuclear weapons is that they make places unlivable. Boom is secondary.
And for Ghouls, not all Ghouls are created straight away, some Ghouls like
Spoiler Moira if you blow up Megaton
are created afterwards. Also the very likely small Ghoul population would of had to contend with the Super Mutant threat, other Ghouls being hostile and other mutating creatures. Also big negative for the Ghouls, they can't have children, their population numbers can't grow beyond Ghouls being created afterwards. You need population growth to have significant change.
The NCR is from Fallout 2. Fallout 2 took place 80 years after Fallout 1, which takes place 80 some years after the bombs dropped. Fallout New Vegas takes place some 40 years after Fallout 2. There's a whole lot of civilization outside of the game world you don't have direct access to. And while New Vegas might not be as developed itself, it accomplished far, far more than anything seen in Fallout 3.
Yet we are talking about the same world, the Brotherhood of Steel and Enclave developed outside of the area the game takes place. Just because the NCR developed on the coast, doesn't change the fact that virtually nothing happened in the New Vegas area in those two hundred years either. Heck New Vegas by some people's logic should have become a metropolis of civilization in those two hundred years, especially considering that virtually no nuclear weapons fell on it thanks to "laser defenses".