When you say "animated banner always gets more clicks" do you mean only animated image or it applies for flashing letters or similar too?
Having movement of some type on the banner will draw people's attention to the banner, so to this end it doesn't matter what it is that's moving. However, after the eyes are drawn to the banner, whether it's the image or the letters that are moving should make a difference, because the moving element will get more attention, which will determine which element will get seen/read first.
It would be interesting to take 3 otherwise-identical banners, animate the image on one, animate the words on another, and animate both image and words on the third, and compare performance. 
Thanks for triggering more banner testing ideas in me!
Amy
I actually did tested the same banner with image moving and image static-letters moving. The latter got better CTR, but the first one was pretty famous banner so I could describe it to novelty.
mostly i think it refers to the image moving.
be careful how much attention u are placing on the CTR, are u able to shift this attention to the actual conversions or profit? thats a more important metric to watch