Microsoft only provides 5 years of mainstream support for any of its products including Windows, and another 5 years of extended support to follow. The extended support is a paid support period. According to this formula, the mainstream support for Windows Server 2008 would be ending in July, 2013.
Let’s first make sure that we know what is mainstream support and extended support.
Mainstream support: In the mainstream support, Microsoft will provide regular security and other product related updates which will be free to install. This includes security patches and service packs.
Extended support: The security updates still remain free and available for all but other updates will be provided only to the paid customers.
The year 2012 is certainly the year of Microsoft has they have been busy releasing updated versions of almost all their products including Windows 8 and Office 2013. As a result of this, Microsoft has extended the mainstream and extended support periods of some of their products including Windows Server 2008. According to Microsoft:
"Modifications to the expiration dates for Windows Server 2008 are a result of the launch of Windows Server 2012, giving customers the additional 2 years of support."
The RTM version of Windows Server 2008 R2 was released on 9th of July, 2009 and the support period was ending on 9th of July, 2013. But now it has been extended by about two more years meaning that now mainstream support for Windows Server 2008 will end in January, 2015.