The last big rts game I remember being released is Anno 2070. And that was last November I think. I don't recall any big names in that genre being released in 2012.
That's because everyone (other than ANNO) is waiting for 2013 (SimCity in particular). Also, ANNO 2070 has the misfortune of trying to escape the LONG shadow that both SimCity and Civilization V have cast over the RTS genre; note that only the latter did anything in 2012, and that was paid DLC.
(I've been alternating between ANNO 2070 and CitiesXL for my RTS fix while waiting to see what SimCity 2013 shapes up to be. Despite ANNO 2070 being cursed with Ubisoft as a publisher, it is actually a decent game; however, what doesn't help, besides Ubisoft as a publisher, are the reality that it is actually a greater system pig than Crysis 2, let alone Civilization V, and the horrific lack of retail findability, let alone purchasability - and especially in the US.)