Note the 2nd last paragraph of the following article:
http://www.pcworld.com/article/2010820/how-long-will-microsoft-support-windows-7.html
"you probably won't have much to worry about with Windows 7 for another seven years."
A lot of users and corporates stuck with XP for so long because Vista was bad and many organisations seem to limit their desktop upgrades to 7 year cycles due to budget constraints. They upgraded from XP to Windows 7.
Windows 8 is so bad I can see a lot of organisations skipping it and upgrading from Windows 7 to Windows 9 (if Win 9 is any good).