Magic

Great - someones managed to write code that can physically unplug a PC from a wall!

If the machines were actually hibernating, then they'd be in the same power state as when they were 'off'. I assume they actually mean in standby mode.

Thing is though, the software probably doesn't save significant power. Any monitor and PC that isn't actually physically switched off at the wall is still in power-down standby, and still drawing power. So they're probably saving zero from the monitors (if they have power saving active), and the saving from the PCs could be minimal.

There's also the small point of the hidden cost in wasted time as everyones PCs turn on, load the OS, and they log in. Over a year this will add up.

Even just setting the machines to hibernate would save some time, and just as much energy. Or alternatively just buy energy efficient PCs and turn the various power saving options on - setting a machine to enter standby after 30 minute inactive would save more power.