They may noy have bothered with random encounters this time, but neither I bothered with them in FO3.
For me, what really matters are the quests, things to actually do in the world, instead of wandering around for hours hoping to find ANY quest at all. This reay bothered me in FO3: so few quests outside the main plot.
That huge world with so little do that matterred, instead of searching for these "precious" random encounters that add nothing at all, IMO.
It is an RPG! RPGS must have quests!
I never understood why Bethesda took this approach with FO3, since their prior game, Oblivion, has truckloads of quests.
New Vegas, on the other hand, feel a live world to me because everywhere you go there is some quest or another, and a good bunch of them are kind of interweaved in subtle ways. It makes me feel important because I am, you know, questing, actively doing things, instead of just looking for a random-spawn-that-may-or-may-not-appear-but-even-if-it-appear-will-add-nothing-at-all-to-the-game-world.