Top posting can be useful but it's generally not recipient-friendly in conversational style correspondence as demonstrated in vocaro's amusing example. And bottom posting is particularly annoying if the sender doesn't trim excess content.

Maybe they don't realize it, but senders who can't take time to compose easily readable messages can be guilty of selfishly transferring the burden of comprehension to recipients. An exception is "sloppy" communication between cooperating senders/recipients.

Unfortunately mail software isn't sophisticated enough to provide recipients more choice of preferred presentation styles for messages they receive regardless of how senders compose them. I don't see any solution to the endless top/bottom/inline posting debate without the software becoming more neutral to different sender and recipient styles.