The story also originally incorrectly presumed the title of Volume III would be "Riders of Rohan," but Turbine has contacted GamerZines to clarify things:
Siege of Mirkwood will arrive in December and will mark the conclusion of Volume II of LOTRO's epic story. We will be kicking off Volume III in our first update of 2010. The story incorrectly presumed that Volume III is called Riders of Rohan. Beyond the fact that Volume III will begin with our next update, we have not released any more details about our plans for the road ahead and we will do so when the time is right.