Also hardware/horsepower. MMO's work at a scale different than 2, 4 or even 8 player games do. Often its not possible, practical or more prone to issues to try

Also hardware/horsepower. MMO's work at a scale different than 2, 4 or even 8 player games do. Often its not possible, practical or more prone to issues to try and have a client only model for some games. Eve Online is a good example of this.