The documentation above states "Some of the default paths may resolve to targets that do not exist on your system." For extensibility authors writing addins or installers for addins, the documentation should explicitly state (rather than loosely imply) that it is therefore necessary and valid to create an addins folder if it doesn't exist.
For example if the folder Addins under %VSCOMMONAPPDATA% + \Microsoft\Visual Studio\<Version> does not exist when an addin installer is being run, then it is necessary and entirely valid, for the installer to create a new subdir called Addins.
Some formal documentation or comment from Microsoft on this subject would be very much appreciated.