Now that Windows 8.1 Update 1 is available for most (well, except those Enterprises relying on WSUS), one topic seems to be the most predominant of the past couple days, and that's what criteria Microsoft uses to display the new Power icon on the Start Screen.
Funny enough, some that aren't seeing the new Power icon after installing Update 1 feel like Microsoft has somehow shafted them. There's been some definite confusion about it, enough to warrant some clarification. There is a sort of rhyme and reason to whether or not the Power icon will be available for your particular computing setup.
The Power icon will show up on the Start Screen for:
Tablets larger than 8.5 inches without Connected Standby
The Power icon will NOT show up on the Start Screen for:
Tablets under 8.5 inches
Tablets with a physical power button and Connected Standby
While the above is being used as the premise for defining when and if a Power icon will install, it's reportedly not set in stone and doesn't seem at all perfect. Some running Surface RT have reported the Power icon being available for them, while others have reported seeing it on a Dell Venue 8 Pro. So, bottom line is that if you have the Power icon shown on your Windows 8.1 Update 1 Start Screen and, based on the established criteria you shouldn't, congratulations! Feel free to gloat about it by strutting around the office.
P.S. Connected Standby is a Microsoft specification for Windows 8 hardware and software. It gives PCs (and devices) the same capability as smartphones, where pushing the power button only puts the device into a "sleep-like" state. In this sleep-like state, network connections are still valid, battery consumption is minimal, and the device can turn on in less than 300 milliseconds.
P.S.S. Richard Hay over at WindowsObserver has posted a method for editing the registry to enable and disable the Power icon anytime you want. Read it here: Add the missing Power Icon on your Surface for Windows 8.1 Update