Amazon now has several listings for Windows 8 upgrades, including a European N edition that is marked as "not with Windows Media Player."
One listing for a Windows 8 Standard Edition to Windows 8 Pro Edition shows that Microsoft will be offering product keys in retail packaging at launch, with no disc required to upgrade to the Pro edition for Windows 8 users. The online retailer hasn't listed any pricing against the Windows 8 listings, but Microsoft has previously said that existing Windows XP, Windows Vista, or Windows 7 users can upgrade to Windows 8 Pro for $39.99 online or $69.99 in stores.
Windows 8 Pro, Upgrade N Version
Windows 8 Standard to Windows 8 Pro Edition
Source: The Verge