The Australian site pcauthority.com has an interesting post about consumer confusion related to the retail version of Windows 8.
Microsoft has made significant changes to the way Windows is being sold. The resulting confusion has retailers claiming that the boxed copies of Windows 8 they are selling are full versions, not upgrades. In fact, they are upgrades. Anyone wishing to purchase a non-upgrade version of Windows 8 can either buy a new computer that comes with an OEM version of Windows 8, or wait until the new “System Builder” version becomes available. The System Builder version is not yet available, and pricing is yet to be confirmed my Microsoft.
The pcauthority.com article explicitly demonstrates that retail boxed copies of Windows 8 cannot be used for new installs. And despite the source being Australian, the same rules apply here in North America.