Visual Studio 2012 already ships with the Windows 8.0 SDK and is used whenever you build using the "v110" platform toolkit. As long as you install VS 2012 Express for Windows Desktop or VS 2012 Pro or later, you have the full SDK for Windows 8.0. And in fact, with the VS 2012 update, you have the Windows 7.1A SDK, and also when using the v110_xp platform toolkit.
Similarly, if you have Visual Studio 2013, you have the SDK for Windows 8.1.
The "manual" part appears when you want to use the Windows 8.x SDK with Visual Studio 2010 or the Windows 8.1 SDK with Visual Studio 2012. See this and this blog post.
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