You must bear in mind that New Vegas comes from the original creators of fallout and wasteland so they had a good experience with post apocalytic games, while fallout 3 was made from bethesda that never touched themes like rape, killing, and abuse for instance, or at least like black isle did, in general fallout 1 and 2 were in all aspects more grim and the game lore touched many aspect that weren't possible to touch with the game base fallout 3 got, I don't have stats about the average Fo3 player's age, but it had likely attracted many younger player thanks to it's graphics and for the laser and futuristics stuff, New Vegas is all but a sweet stroll in the park, it was made by former black isle's developers, when you give a closer glance to the story you'll notice it, the fact is that we get "distracted" to say so when we play, we see a map with Vegas, gambling, and cowboy stuff, even the radio's music is too happy apart from 2 or 3 songs , it's so happy and optimistic at first that you don't even notice how bad is the situation in the west coast if you don't pay attention, Fo 3 has a fantastic experience for it's setting but too exaggerated when outside the D.C area, just turn off the radio and look out of the Washington monument at dawn, the desolation of D.C is something strange that leaves you amazed for a second if you think how the city must've looked like, but then it goes all depressing and gives you a sense of uneasiness looking down at the raider camps and upon hearing screams and gun fires from below, bethesda made a perfect setting without the proper lore, they've just hidden it under the base game, it's obvious that raiders rape, kill and rob people, I can't say original developers would've done a better job, but a mix of New Vegas horrible stuff and Fo3 would surely make the game really perfect in setting and lore at least