Usually when Microsoft launch a new flavour of Windows the previous version is available preinstalled on new machines for at least another two years. It’s different with Windows 10!
Windows 7 Professional will be available until 31 October 2016 (4 years after the launch of Windows 8) while Windows 8.1 will also be available until 31 October 2016 but that’s a mere 15 months after the launch of Windows 10.
The end of Windows 8 comes even quicker at 30 June 2016. Microsoft’s Windows lifecycle fact sheet has all the details: http://bit.ly/1MGslQR.
Friday 31st October 2014 sees End of Sales for certain flavours of the Windows client: Windows 8 will no longer be able through the Retail channel, and Windows 7 Home Basic, Home Premium, and Ultimate cease to be available pre-installed.
However, there are no End of Sales dates yet published for Windows 7 Professional or Windows 8 acquired through the OEM channel, which means that these products will be available for at least another year.
See the Windows Lifecycle Fact Sheet for all the dates: http://bit.ly/1FUEAsX.
An interesting Microsoft article on how the MAP Toolkit can help you identify a mis-licensed computer (one using a Windows VL licence but that did not ship with an OEM-installed version of Windows) and a mis-versioned computer (one using a Windows VL licence but that did not ship with a qualifying OEM-installed version of Windows): http://bit.ly/QnvizU.