I agree with you their - but animations come with a number of restrictions that brute force code can overcome. The biggest problem would be varying things from a small breeze to a brisk wind to a hurricane.

Also you have to be careful with your orientation of models, which will cause you to either create more models, or have a bunch of cookie cutter models.

One thing you might also look into as opposed to messing with all the vertexes (and I should have emntioned it before - since I am currently examining the feasibility between 20 or so other things ) is the use of bones. This will give you a hinge in your model already - then you just assign a few skills and a variable that gets set by the weather man, and you should be able to pull off swaying lanterns, trees, grass... Though bones require a bit of CPU time to calculate the position of the vertexes... Ah well - bump up those minimum requirements, and you are good to go.