I took the 'every' portion to mean that every screen locker is affected on the vulnerable versions of Xorg server, not that every version of Xorg is affected.

Meaning that any version of any of Gnome/KDE/XFCE/etc's screen lockers will be defeated by this exploit if they are running in this version of Xorg.

As far as I can tell this is probably true, unless someone knows a locker that uses an alternative method of locking out all keyboard/mouse input?