Moria and Mirkwood both include the instance cluster in the quest pack. Moria EXPANSION also includes the Warden and Rune-keeper classes. Mirkwood does not have an EXPANSION pack because the expansion did not bundle anything with it. It was released as a quest pack and labeled as an expansion .
After Mirkwood, Turbine realized it could make more money buy making people purchase the instance cluster separately, so the instance cluster became a featured selling point of the expansion instead of something we took for granted to be in it. So for the next expansions, Rise of Isengard and Riders of Rohan, the EXPANSION includes quests, deeds, and the instance cluster. The quest packs only include quests and deeds.
[CENTER][SIZE=1]MINSTREL and member of the vocal minority[/SIZE][/CENTER]