ICCCM Window Deletion

[Russell Shaw]

Hi,
In the ICCCM, it says:

   4.2.8.1. Window Deletion
   Clients, usually those with multiple top-level windows, whose server connection
   must survive the deletion of some of their top-level windows, should include the
   atom WM_DELETE_WINDOW in the WM_PROTOCOLS property on each such window. They will
   receive a ClientMessage event as described above whose data[0] field is
   WM_DELETE_WINDOW.

Why does destroying a client top-level window terminate the server connection if it
has more than one top-level window?