It's not unusual for people to use one monitor when setting up a box and another monitor when deploying, in our case it took a few minutes to realize that deleting the /etc/X11/XF86Config was required to get r-c-xfree86 to do the right thing.
I suppose it would be really neat to detect that X is failing altogether, and offer to wipe (or back up the config) and start the config automagically, but perhaps such a thing is for another day.