Going by this Windows lifecycle page on Microsoft, Vista mainstream support actually ended April 2012. This probably explains why Internet Explorer 11 and Office 2013 cannot be installed on Windows Vista, as they were launched after that date. The end of extended support for Windows 7 is January 2020. By then I'm sure Microsoft is going to face the same XP-like problem all over again, but this time getting people off Windows 7 to whatever is out then.
In my opinion, I'd consider Windows 7 mainstream support already at an end up for most coming products, as the next version of Office is likely to be 2016 (based on its 3 year cycle) and there's no sign of an IE12 beta yet. I also doubt Microsoft will consider adding support of Windows 8 apps in Windows 7, not that I care anyway. :disagree: