Getting rid of the GWX Win10 installer nag thing isn't difficult for most users here, but by and large, I'd say 3/4 of the PC users out there even if shown the directions after googling how to do it, wouldn't get it right OR wouldn't consider doing it as it's that "computer code magic stuff" or whatever. Geek Squad and other places are LOVING this right now, as there have been more than a few cases of Win10 bricking PCs doing the auto update on its own.
Also, consider businesses that are running older versions of Windows because they are using finicky other software/hardware things with those systems specific to their company - you know the types of things I'm talking about, and they are numerous. What happens when Win10 just starts installing on all of those? Mark my words, that'll be a big story if/when it happens. Already it's growing just from home users who have PCs/Software that isn't working great with Win10 and having a surprise upgrade.
Not to mention, the loss of personal photos, lost loved ones videos/etc, being lost on bricked PCs due to Win10 auto updating/installing and then bricking - can you spell class action suit, as there is no price that can be put on stuff like that.
Also, there have been reports that even with the Get Win10/GWX stuff completely disabled, some PCs are being "upgraded" to Win10 from older versions of Windows if they have auto updates enabled. When challenged about this, Microsoft's answer was "just turn off autoupdates". Great, so no automatic security updates then. Linus Tech Talk specifically went into all that last night on their WAN show, the video for which should be up today some time, with screen shots/proof of this happening to people.