I really like how you made the options really slick in the taskbar but don't forget that a shutdown button already exists on Windows 8 devices. It's the hardware button which, by default, runs the shutdown command when you tap it. It's how I have taught people to shutdown their machines since Windows 95 (I think).
The first poster also mentioned pressing Alt-F4 from the desktop. That is another good option. Both these shortcuts have worked for the last several versions of Windows.
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