You have not missed anything, it's me who forgot to mention in the tutorial that an upgraded Windows cannot be sysprepped. I added this warning now to tutorial:
Originally Posted by Steveyg777
An upgraded Windows cannot be sysprepped. As this method is based in sysprepping, this tutorial is valid only for Windows setups which have not been upgraded.
This means that if you have for instance in-place upgraded Vista or Seven to Eight you cannot sysprep and this tutorial cannot be used in your case. The same applies if you have upgraded Windows 8 to Windows 8 Pro.
Notice that a repair install is also an upgrade install, so if you have ever done a repair install (= in-place upgrade to same edition), you cannot sysprep.