Turbine is, without a doubt, the most value-for-money-orientated MMO developer in the market. There are no more spoiled subscribers than LOTRO-ites, who wallow in a new bundle of content every month as part of their monthly tithe. Which is why it's slightly quizzical that Turbine would - at the most challenging time of the year in gaming, let alone on the doorstep of the Lich King himself - throw out its first paid-for expansion since Asheron's Call 2: Legions.
The answer is actually rather simple: scale. With the Mines of Moria, Turbine has extended Lord of the Rings Online beyond the Shadows of Angmar. While many expansions (including Wrath of the Lich King) try their best to create an 'open world', and, in the process, a degree of storytelling ability, the Mines of Moria so far gladly leads players by the hand to areas of interest without managing to lose the first M in MMO.