Windows 8.1 Update 1 is out, and with quite a few improvements. However, the Start screen's power button only shows up on some devices. Our friends at Hackerspace has a guide to hiding it if you don't want to see it (and showing it if you do).
Now you've updated your Windows 8.1 to Windows 8.1 Update you'll notice a couple of differences between the two. One that annoyed me at first was that the Power button appeared on my laptop but not on my Surface RT. To me it would be more use on a tablet than a laptop where I can just close the lid. Here's a fix, and this being Windows it involves the registry so stop here if you don't go there.
First start the registry editor by typing regedit into the search box on the start screen.
Then navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\ImmersiveShell
Right click on ImmersiveShell and create a new key called Launcher
Now right click in the right pane and select DWORD (32-bit) Value. Call it Launcher_ShowPowerButtonOnStartScreen
Set to zero and the power button won't show; set to one and you got it!
You'll have to restart your tablet after making the change.