I can see the reasons why this option is not available.
Take this into account. I Quote you, your name shows up in the quote I just did. You change your user name.
People browse thread later and become confused, because I am quoting a user that does not exist anymore.
The only way they could fix this problem is quote a user id number and have php sort out a sql query when it builds the thread page.
But why do this when its just going to be confusing for moderators, to keep a eye on people causing trouble.
edit on 13-11-2012 by amraks because: (no reason given)