This is probably a stupid questions but the gnome screensaver FAQ says:

Why gnome-screensaver, what happened to xscreensaver?

gnome-screensaver is a new screensaver that can replace xscreensaver. It is designed to integrate well with the desktop and provide a control interface that is desktop neutral. It simplifies and streamlines the experience for the user and provides more capability for the system administrator and vendor.
It is designed to support:
  • a desktop neutral control interface via DBus
  • a desktop neutral and standard way to install and manage screensaver themes
  • switching users directly from the unlock dialog
  • allowing a system administrator to set a mandatory policy for any setting
  • a secure separation of user input processing and authentication from the screen locking window
  • a separation between the screensaver theme engine and the theme settings
  • integration with the desktop (themes, fonts, toolkit)
  • translation into many languages by the GNOME Translation Project
  • instantly applying settings changes
Does "allowing a system administrator to set a mandatory policy for any setting" mean that the Ubuntu devs could have just turned off the extra features and they can be turned back on, or is it really impossible to get all the features of xscreensaver in gnome-screensaver.