While primarily for business customers, Microsoft does have the option to downgrade your Windows 8 Pro Installation to Windows 7.
Another benefit this provides, is if you happen to find yourself in the unfortunate situation of being on a Home Edition of Windows Vista, you may upgrade to Windows 7 Home and retain all settings, after doing the upgrade to Windows 8, still retaining all settings, you may then downgrade to Windows 7 Pro. Thus doing the impossible, and going from Windows Vista Home to Windows 7 Pro and changing actual product lines (should you need the features of Pro and already own a valid license).