That deal requires the earlier OS to be installed, so it's an update install. These have never been a good thing in the past, there's always something left behind from the old OS that later turns up to break something in bizarre ways.
It also requires a complete reinstall of all software unless the previous OS was Win7 - this is probaly to minimise the number of support calls arising from from updating an OS rather than starting from a clean disk.
This is the worst of both worlds, no clean OS install & having to reinstall all software. And, if in the future you want to completely reinstall Win 8 after formatting the disk you'll have to install XP/Vista etc first (let's play hunt the old OS dvd).
CakeAlexS
Here's a link, it will be cheaper to download on Friday....
http://www.microsoftstore.com/store/msstore/html/pbpage.Windows_8_Pro
PS If someone had made a habit of saving a few bucks over the years by only buying update versions of Windows the "clean" reinstall of this Win 8 could go, install Win 3, update to Win3.1, update to Win 95, update to Win98, update to Win98SE, update to Win Me, update to Win XP, install XP SP3, update to Win 8. What could possibly go wrong? ;)
edit for appalling typing