The Xclients script has a catchall at the bottom, which runs RunWM --Fvwm95, and then, if this returns an error, runs fvwm. However, RunWM won't return an error, as if Fvwm95 isn't found, it runs twm instead, and so Xclients never gets the chance to exec fvwm.
Unfortunately the current settings in the AnotherLevel do not permit running on a system without fvwm2 installed at all. If RunWM will return an error when no fvwm2 is installed the window makangers switching can experience problems. It is far easier to use the .Xclients for those die-hard old-days fvwm people.