There’s a hidden feature in Windows 8.1 that for some reason (marketing?!) didn’t get public-ish… It’s slide-to-shutdown. Basically, just like on Windows phone, with slide-to-shutdown you have the option of shutting down your PC from sliding down the lock screen.
This ‘feature’ is however available on your Windows 8.1 PC by running the slidetoshutdown.exe. You can do this directly from you Run prompt or by running slidetoshutdown.exe from a custom app you might develop for yourself (and the rest of the world ).