OK, for reference, my startx is attached as well (XFree86 4.2.0). The differences are too many to make the fix as simple as I thought it was going to be. Your file, for instance, doesn't even bother trying to set defaults (regardless of whether defaultserver is set or not) if there is no xserverrc or .xserverrc file.
Creating the symlink /etc/X11/X pointing at /usr/X11R6/bin/XFree86 would probably be the easiest way to fix it now. Although creating a ~/.xserverrc containing the line exec /usr/X11R6/bin/XFree86 might work as well. But if this is a multiuser system where more than one user should be allowed to start up X, then you're going to want the system default xserverrc file (the one in /etc/X11/xinit) to contain that line instead. Any of the three *should* work.