Xorg driver change Xv tvout enable attribute automatically (when tvout cable is plugin/unplugged). "Old" tvout desktop widget listening for Xv attributes changes so it update button text ON/OFF. Auto enable/disable tvout output is done by Xorg driver (not software, daemon or tvout widget).
Status menu plugin using same code for Xv attributes, so it should update gconf key when Xorg driver disable tvout output. Desktop widget now monitor only gconf keys, so if you did not see that button ON/OFF changed, there is problem in status menu widget...
I think that in status menu widget is some race condition (and that is maybe reason why is not working):
Xv enable attrbite was changed --> run callback function which should update gconf key
and when gconf key is changed --> run callback function which should update Xv attributes (and Xorg driver will enable/disable output)