Today we are told that the 8.1 update, (a version which allows you to keep apps, settings, and files), is officially being rolled out worldwide. No longer will you have to do a clean OS install, to go from 8 to 8.1.

But I don't see the update inside my (Enterprise's) desktop 'Windows Update' program, and furthermore, Microsoft themselves say:

If you’re running [Enterprise], you can't install the free update to Windows 8.1 or Windows RT 8.1 from the Store.

However they DO also say:

If you installed Windows 8 using an MSDN ISO, you might be able to install Windows 8.1 using a similar ISO from MSDN

But it does not specify whether this method allows seamless apps and settings-retaining upgrading or not.

Is there a method for doing it (whether official or unofficial - perhaps confirmed via experience of updating with some sort of Enterprise 8.1 ISO), or is an update indeed expected for the Enterprise version via the desktop 'Windows Update' program?

A further observation which may help: the page I cite refers to the 'Windows Store', which is the 'Modern UI' app store and NOT the desktop 'Windows Update' program which typically updates desktop Office and desktop Windows alike.