Originally Posted by Alrik Fassbauer 
I wonder why no-one has yet implemented different AI as a means to increase the challenging ?
I think that's because it has the risk of 'low difficulty' being confused with 'dumb ai'. Low difficulty isn't a 'bad' thing by default - dumb ai is.
I'm with DArtagnan on this one, however I'm thinking that pacing might be, up to some extend, relevant to each player's speed, in which case offering a lower difficulty setting for those who can't keep up wouldn't hurt the game.