Many of the problems are attributable to the use of the Gamebryo engine, which isn't quite perfect, but was the best they considered to work with for the purpose of the game.
The other thing to bear in mind is do you have any idea how much coding likely went into the game? The sheer amount of scripting that has to be coded combined with the fact that the game is intended to be an "open-world" affair means lots of possibilities, plenty that were likely unintended (like in FO3 the wonderful physics glitch for deathclaws vs. rocks -- deathclaws go flying straight up into the air and "disappear" entirely).
You don't see the kinds of bugs and glitches in other games like you do in FO3 and NV mainly because most other games are what you could call a "closed" environment, where nearly everything is scripted to happen a certain way, every time, kind of like the movie "Groundhog Day."
I really wish more people actually understood games design and coding.