Well, it’s official. Proof, if ever proof were needed, that Microsoft really hates you. Or, at least, cares so little for you that it’s willing to not only severly limit what you’re able to do, but that it also wants to waste your time.
(This contrasts with all previous versions of Windows, where you could simply insert the CD from a previous edition of Windows to allow the upgrade to install)
This makes restoring a working system after some form of failure a much longer process – since two OS need to be installed rather than one.