After posting this I went and read this article which shows going a fresh install.
Considering it's just $70 for Win8 Pro I'd rather just buy the box so I can easily do a fresh install like this (I'm assuming the $70 retail box from Staples is not also an upgrade DVD).
Tough luck. It is the upgrade DVD (and the upgrade key). Notice all the "upgrading" on the homepage.
But exactly the way it needs to be done. In the NT5 days you only needed to provide the CD of the previous version at installation - but the upgrading has been re-imagined since then.