<p>What if you inadvertently change the meaning of your post?  E.g., you leave out a "not" in a statement or you add (or remove) an ambiguity.  The thread could stand for a long time (and perhaps be viewed and referenced by many visitors) before anybody noticed the change.  Because what you write is always in the context of a thread of replies, comments, and votes, people <em>must</em> have an opportunity to see that a change has occurred, no matter how seemingly minor, and be able to react appropriately.  The current system seems to be a gentle compromise between the advisability of such a mechanism and the need to keep the volume of system messages down to a manageable level.</p>
