It may have been clear to you but that doesn't mean that it is clearly established here and cannot be done.
Please cite where Users have failed using Anytime key to clean reinstall the higher version.
MS also says retail Upgrade version must have an activated copy of Windows installed but there is a workaround for those not wanting to install the qualifying version or installing to a cleaned or new HD. In addition the installer will accept Upgrade version key upfront if any version of Windows is detected on the drive.