While I see your point, I think AI may be banned in those universes for the same reason that time-travelling devices tend to be written out of sci-fi and fantasy: Stories are better without them. (If one counts the ever unfolding history of the world as a story, my counter-point actually validates your original point. Touché.)
Those broads limitations also make writing the stories easier, since the author/worldbuilder doesn't have to come up with 100 different reasons why it can't be done for each particular case. He only have to do it once.
