Brand new clean FC5 install here on a new laptop...
I have the same problem. I edited /etc/X11/xdm/kdmrc (also pointed to by /etc/kde/kdm/kdmrc), found the aformentioned line, and commented it out. And Xorg still runs with a -nolisten as seen from my process list:
/usr/bin/Xorg :0 -audit 0 -auth /var/gdm/:0.Xauth -nolisten tcp vt7
I've grep'd all over the place looking for "nolisten". Where else could this be getting turned on?