you don't get it...end game slides have NOTHING to do with the static game world, no random encounters, no random events, hardly any enemies on the map, you're neutral to everyone, no super mutants to kill, no raiders to kill, no enclave or equivelant to fight, most of the map world is very empty and you think just because the game has different end game slides that somehow thats gonna offset the boring map world, well obviously it doesn't cause the game has lost its mass appeal and threads keep popping up on how boring the game becomes after a short time, so obviously the game has some serious flaws.
Hardly see how a dungeon has more replayability than a quest.
A dungeon is over once you've gone through it, ain't gonna be much else to do down there the other playthrougs except farm exp and loot mediocre crap.
A quest, which New Vegas has an abundance of, can offer various scenarios.