Visually it would look kinda sloppy, and I'm betting somebody spent some amount of time picking those emoticons so they all lined up neatly like that. But I don't care, I'm just betting you that all the mods would disagree to it.
I'm not too sure what's happening with the smilies and the impending release of TWHL3, the original plan was to have them all redone as sexy AA'd .png's, but that would create problems with IE users. Probably something for later down the track.
There won't be any animated smileys in TWHL3, because:
a) They just add to the amount that needs to load. b) They can be an eyesore. b) All the smileys will eventually be updated/redrawn into transparent png's, obviously lacking the ability to be animated.