> but I would never have considered Markov processes to be an adequate predictability model for natural language

Isn't it the case that for very short distances (several elements), power decay and exponential decay are (or can be made, with proper constants) more similar? Thus, if predictive models were originally studied only for very short sequences in the past (limited computational resources!), it seems to make sense that this is a mistake that anyone could have made more easily back then.