Comment 2 for bug 1013945

So, it's just the way how the settings-GUI is showing you this value.

When set to "never" -> the key from xfconf disappears
When set to "#a number#" -> the key represents the minutes to wait until sleeping

If you look in the source (-> http://git.xfce.org/xfce/xfce4-power-manager/tag/?id=xfce4-power-manager-1.2.0), you'll see that a value equal to "14" will set the timeout to "never". Written in the "xfpm-manager.c"-file