Reminds me the story with Simcity, where EA claimed that it must be always online because NPCs AI is too complex and needs to be handled by servers. And some time later enthusiasts managed to launch the game in offline mode just fine, with zero changes in NPC behaviorYes, I think this comes most likely close to the point. AI needs CPU power. I would not be surprised, when the AI features will come with the multiplayer. Then the AI could be processed by the server.
I suggest you to play the newest Hitman games. Then you'll know what modern CPUs can do with AI when good programmers are involved, even if there are hundreds of NPCs.