Microsoft has posted up an official statement where it offers some clarity on the install rights of the stand alone Office 2013 product compared to Office 2010 and the new Office 365 From Neowin:

A blog post written by Jevon Fark, a senior marketing manager for Microsoft's Office Division, states Office 2013 install rights are the same as the Product Key Card versions of the older Office 2010, meaning the rights are only for one PC for the life of that computer. Fark added, "In the event that a customer buys the Office 2013 software and installs it on a PC that fails under warranty, the customer can contact support to receive an exemption to activate the Office 2013 software on the replacement PC."

The full package product versions of Office 2010 did allow three PC installations for the Home and Student version, along with two installations each for the Home and Business and Professional versions and all of them had transfer rights. In other words, if you really want a stand-alone version of Office that can also be installed on one that more PC, you might want to buy the older FPP versions of Office 2010 while you still can.

 Microsoft offers clarity on Office 2013 and Office 365 install rights