ICCCM Window Deletion

[Russell Shaw <rjshaw netspace net au>]

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?