It's not stylistic. As far as thought processes go, keeping posts for conversation chains on individual posts is the easiest way to keep track for the poster. It's not a problem if you're just responding to a topic, but it can be a problem if you're the thread creator and you're attempting to keep track of various side themes. Granted, most topic chains here are far from mind bending and this is just a preference, but there are some rare circumstances where this could actually interfere with the topic.