I doubt Bethesda could create a game as complicated as that, lol. Most likely, anything 100 feet behind and in front will probably be paused.
That pausing isn't even the case in Oblivion, AI updates on almost all named NPC's throughout the game world even when you're not there, but not constantly to save resources. It has different AI processing levels, which is mostly based on distance. NPC's in actively loaded cells will update every frame, NPC's in cells you just left update every so many seconds, and NPC's in very distant places update every so many minutes, with 15 minutes being the max.
So you're wrong, it wouldn't be hard for Bethesda to implement this. But I'm pretty sure they haven't, as only a small minority of roleplayers would enjoy such random attacks in low level processing.