In a response to user outcry, Microsoft has made Office 2013 licenses transferable.
Updated transferability provision to the Retail License Terms of the Software License Agreement for Microsoft Office 2013 Desktop Application Software:
Can I transfer the software to another computer or user? You may transfer the software to another computer that belongs to you, but not more than one time every 90 days (except due to hardware failure, in which case you may transfer sooner). If you transfer the software to another computer, that other computer becomes the “licensed computer.” You may also transfer the software (together with the license) to a computer owned by someone else if a) you are the first licensed user of the software and b) the new user agrees to the terms of this agreement before the transfer. Any time you transfer the software to a new computer, you must remove the software from the prior computer and you may not retain any copies.