Honestly, I have no idea. I have been told it is basically the same thing, but Wetta Did tons of Development and Created Massive. Each of the Characters have thousuands of "if-then" type controls basicaly their own little mind.These statements then controlled animation clips that can be made in Maya, using the Trax editor and stuff... For instance, if one were to shoot an arrow at an enemy and it missed, it would try to redirrect its path for a better shot, they even had characters run away when they got scarred! pretty powerfull software. Massive (like AI is a plugin for Maya. It is used within Maya.
Brian