Windows, being a commercial OS, is subject to Microsoft's control over when and whether you can get a copy. A few days ago the dates for the ending of retail and OEM availability of Windows 7 were announced, and then Microsoft backtracked. 

It is obviously in Microsoft's interests to stop selling previous versions of Windows as soon as possible after the new version appears and users are generally happy with this - but only if the new version is thought to be better than the old. Microsoft has traditionally set different dates for stopping retail sales of the OS and OEM use of the OS in new machines. This makes sense because if a manufacturer has designed some hardware that works specifically with the soon to be phased out OS they need time to clear their inventory of existing machines and design a new model for the new OS. 

Last week Microsoft announced the timings for Windows 7. For retail sales the date was October 30 2013, so if you wanted a copy you have missed the boat. Not in reality, however, because at the moment you can still buy a boxed copy from many retailers who still have stock. 

The date for ending sales of Window 7 preinstalled on new machines was announced as October 30,2014  which is a much more important date in the life of an OS. Soon afterwards Microsoft announced that this was an error and the date was to be determined. 

What is surprising is not the date but that Microsoft backtracked and is now thinking about it. The date announced is in line with the dates for previous versions of Windows. 

The timings for other versions for end of retail following the release of the next version are: 

So you can see that, apart from XP which was given a little longer to live, the rule is that the previous version is phased out of retail about a year after the new version. 

The same data for time to end of OEM preinstalled sales is only available for the XP to Vista and Vista to Window 7 changeover - 3.7 years and 2 years respectively. Again XP had a bit longer because Vista wasn't suitable for smaller machines such as netbooks.Using the 2 years value, October 2014 is exactly when Windows 7 OEM preinstalled sales should end. 

Now you can appreciate why Microsoft's backtracking is strange. Could it be that it all depends on how the take up of Windows 8.1 goes?

As to end of support the  relevant dates are: 

Extended support basically means "security updates" and there's a 5 year gap between mainstream and extended support. It could well be that customers will be asking Microsoft will extend mainstream support for Windows 7 on the grounds that Windows 8 isn't a suitable enterprise operating system. January 2015 seems very close all of a sudden.