Thanks! Turns out I didn't. I expected gdm not to be a separate package,
and/or to be automatically installed when selecting Gnome for X during
initial installation. Now with /etc/sysconfig/desktop as above, init 5
starts gdm, which does allow root login.
I will point out from a security point of view, do not log into your system as root, except for specific purposes and for very short time periods. I use the login as an ordinary user, open a terminal session, and then su - or sudo to get to a root session. As far as KDM not allowing root logins, this may be for security reasons as stated above.
-- James McKenzie
