given my preceding post, i think a greatly overlooked affordance of fictive worlds (as opposed to virtual environments) such as WoW and Second Life is that their dimensionality and persistence ground avataric performance in-game / in-world, and therefore give critical socio-cultural context to identity-appropriation and -evolution.
that is to say, there is much, much more to the third dimension, than simply the extrusion of topologies-for-learning along the z-axis.