root gdm login enabled as default in RHEL 6.2

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I just did a clean install of RHEL 6.2 workstation and created an empty /etc/securetty.

On a whim, I decided to see if root could login via the graphical login (even though I'm used to root gdm login being disabled by default).  I was surprised to see that I could login as root via the graphical login. This seems a security risk to me.
I double-checked that /etc/pam.d/gdm had the following:
auth       required user != root quiet
This should disable root gdm login but it doesn't.
Not sure if RH meant for root gdm login to be enabled as a default. Documentation isn't clear but it would seem strange to me if this is the desired default. 
Any advice on how to disable root gdm login would be appreciated.