Here's more ammo for Eileen to hate flat mode:)
In order to give a link back to the original message in flat mode, we have to know what page that message is going to be on. And since each user can be different, without doing some heavy calculations this couldn't be done.
Now, if maybe if the links opened in a new window and pointed to showthreaded, it could be done.
<A HREF="http://www.wcsoft.net" target="_new">http://www.wcsoft.net</A>