Currently, lxsession-logout supports the following mechanisms.
- HAL (obsolete) for Shutdown, Reboot, Suspend and Hibernate.
- ConsoleKit (deprecated on some distros) for ShutDown and Reboot. *
- UPower for Suspend and Hibernate.
* ArchLinux no longer supports ConsoleKit and recommends systemd-logind instead (https://www.archlinux.org/news/consolekit-replaced-by-logind/).
Therefore Shutdown and Reboot are only supported by obsolete or deprecated mechanisms.