Office retail licenses could... up until 2013 ... be moved from computer to computer.
Apparently...not any more. Check out the 2013 retail EULA:
Office 2013 Software License Agreement - Office Watch: http://news.office-watch.com/t/n.aspx?a=1782 Under our license we grant you the right to install and run that one copy on one computer (the licensed computer) for use by one person at a time, but only if you comply with all the terms of this agreement. Our software license is permanently assigned to the licensed computer You may not transfer the software to another computer or user.