I think in Skyrim there is only a certain distance range of animated veg/trees. Not sure if it animates behind the player or not since you can whip around pretty quickly... so not sure if there is any process occurring depending on which way you face. But i did notice in far distance things like grass doesn't seem to animate. Which is an adjustable feature in its quality settings.
Skyrim deals with a lot of vegetation and yet functions on a wide range of machines. I think its in part to play with the smart ways they go about tackling performance/quality.
They do something like this using Radial Distance:
Grass
20,000 = no grass, no animations, no shaders
10,000 = no animations, no shaders
5,000 = no shaders
i7 -2600 CPU @ 3.40GHz - Windows 7 - 8GB RAM - Nivida GeForce 420 GT