mainstream support
I don't think you've read this right.
Microsoft have extended the mainstream support i.e. the product will still be in mainstream support until 2015 after that it will transition to extended support. Where it will receive fixes right up until 2020.
What's interesting here is that microsoft are treating 2012 as the replacement to 2008 rather than 2008R2.
I would imagine far more people are using 2008R2 than 2008
Of course none of this is important, the only important upcoming dates are 2014 for XP and 2015 for 2003 after which there will be no more support for IE6 and the browser can finally be forgotten about.