Animation lighting is important, but whether the clouds are high detail or not is of much less importance in an animation, unless the focal point is the clouds. But, mostly clouds and atmosphere are background or clouds are whizzing by as someone flies past them or someone is racing down a street - having high quality at that point needs to be on the focal point. Even the ground doesn't need to be high quality. Ask someone who has created an animation with a PC (or Mac) how high the quality is on the ground. I think it's a mistake to think otherwise.
Of course, if you have an ILM rendering machine, who cares? But, I'm talking to people who are mostly like me - running a PC (Mac) or two.
