I think prophetic is commonly used in this case. Is it that you believe the term has more of a mystical flavor and less of a "reasonable inference" flavor?

Not quite, FF - it's more about the quality of the prophecy. And the same applies to futurology tsuwm.

It's like some people are prone to make predictions which are essentially on a straight line from the present, with no surprises or quantum leaps. Reality never works like that, of course.

I suppose if futurology is taken as "straight line prediction" and prophecy as fairly accurate "quantum leap" prediction, you could say

Arthur C Clarke is more prophet than futurologist
or
Gerry Anderson takes a futurological approach to his stories

Hmmm.

I suppose I'm looking for a word for the tendency to straight line prediction, to put it another way.

I thought this would make my brain hurt