According to the German website Winfuture, Microsoft has decided that Office 2013 (also known as Office 15) will not run on Windows XP and Vista. Microsoft's latest office suite will only run on Windows 7 and Windows 8 systems. Winfuture refers to a trusted source close to Microsoft, but unfortunately the website is not able to disclose any reasoning behind the decision.
An educated guess could be the ending support for Windows XP and Windows Vista. Support for Windows XP will be stopped in April 2014, Vista support is only available for paying business customers until 2017, support for consumers is already no longer available since April this year.
While not much information on Office 2013 has been disclosed, Winfuture also reports that Office 2013 will have a stronger integration with external services using widgets. An example where this could be useful is when making an appointment the widget is able to display the weather information for the location and time of the appointments. Office 2013 will likely be released in Q4 2012 or Q1 2013.
The first public beta release is expected later this month.
