Depends though .. I am not sure if Beth is exceptional in that area of if they simply do more of what is already pretty much a standart, as I guess every game engine can do it if you want it. I simply don't know enough about it and Bethesdas programmers.
As someone else already said, there are not many hikking/cave simulators out there that do it to the same extend as Beth. And that probably for a reason. Virtualy NO Beth game, except for Morrowind maybe, doesn't have certain fixes by the community, like memory fixes and other changes to avoid save game bload, save game crashes etc. It does seem to be a problem.
Sure you can visit "different" areas but majority of caves and dungeons are cookie cutter layouts which have the same linear layout with minor differences besides the big towns or landmarks.
Same with the AI packages, the AI go from home to their destination then stand around in the same spot until it's told to go back home to bed until the next day with minor tweaks.
I apologize if I sound like i'm being hostile(I hope i'm not) and it may just be my opinion but it doesn't that great when the AI is too braindead to realize chasing a dragon in no armor and an iron dagger is something an old lady wouldn't do and the buildings are almost all the same with bland interiors.
That's ok! I find their way of making games pretty ridiciulous as well. So no arguing from my side. I don't think their games really get that much benefit from their you-can-pick-up-even-a-fork! design-idea. But that's not the point. It was more about the question why Crysis made no clue several years ago looks better than F4 - I guess?. And the answer is rather obvious. Different goals in the game design with a different emphasis in the engine. Like I said, all the stuff from above puts simply more strain on the engine in different areas. What ever if that makes senese or not is a completely different question now