Talk:Bending Arts/@comment-99.240.12.41-20100908184159/@comment-153.104.224.87-20100911055612

At a guess, I'd say it's because air and earth are more focused on response, while water and fire pay more attention to flow. Air focuses on diverting and avoiding attacks while earth intercepts and overpowers attacks. However, water and fire focus on the flow, which is more closely related to the energy of their attacks than their existence, since flow is determined by motion and intensity. Water has a tendency to cool which shows in it's bending style's ability to switch to defense in the middle of an attack. Fire has a tendency to heat up (duh) which is crucial to maintaining a steady stream of powerful attacks, stoking the energy of the user and their surroundings to ensure there's enough power to call on.

I know that technically, none of that answers the question, but hopefully it provides the understanding needed to grasp the answer: It's all a matter of philosophy. Besides, the Avatar renders the point moot by being able to perform all the bending arts anyway =P