DF is very complex as a simulation indeed with all the factors influencing the simulation and the amount of feedback taking place. DF is not complex as a game because there are not many factors influencing the gameplay directly that require attention. As soon as the connection between the simulation and the gameplay becomes stronger (for example, with the caravan arc) then Df will also become complex as a game.
I am sorry for causing this confusion, but I was thinking of MMO's as, well, games and thus applied the factors that would make the gameplay of a game complex to DF as well. I am sorry if I offended someone.
Also, it's funny you should mention WoW, as I do not know much of it and thus can't judge if it's relevant to keep tabs on the kind of spells your opponents will be using. That's why I used Mechwarior as an example, because it is relevant to keep track of your and your opponents weapons there. If it would not be, the game would not be complex as a game (I'll keep repeating that from now on to avoid offending people again).
However it is interesting to think about your view, seeing game complexity as defined by the complexity of their simulation, since that means there is not much relation between the gameplay of a game and it's complexity. Take for example Xcom. One could argue that the simulation in this case is really simplistic, meaning for example that a game like Civilisation 4 is much more complex due to the more intricate interaction between all the elements in Civ as compared to Xcom.