Which came first the chicken or the egg?
Why do we drive on parkways and park on driveways?
Sorry I have nothing else to add as I don't own a cat, but I found this interesting, don't think the butter matters but the distance of the fall does.
"The uniqueness of the cat's skeleton is one of the reasons they can right themselves so quickly. Cats do not have a collarbone, and the bones in their backbone have more mobility than in many other animals. For these reasons, cats have free movement of their front legs and they can easily bend and rotate their bodies. This allows them to land feet first. Their feet and legs can cushion the impact. This righting reflex begins to appear at 3-4 weeks of age, and is perfected at 7 weeks."
http://www.peteducation.com/article.cfm?cls=1&cat=1313&articleid=1106