Of course, the major difference is the word "service." If Netflix can broaden its users horizons, the user will be compelled to increase his subscription rate in order to take greater advantage of it. Therefore, while Amazon tends to suggest an increasingly narrow subject focus, Netflix benefits from encouraging a wider field of subjects.
The former has a negative trajectory. By suggesting more of the same, that one method is dependent upon the user's will to seek out new subjects. If he does not do so himself, it leads him to the inevitable conclusion that he has read "everything." He therefore forms his worldview around a limited knowledge base. If you like John Grisham, and Amazon only suggests other books like his, then you are bound to think the world is rife with conspiracy and crime.
The latter has a positive trajectory. By suggesting increasing variety, such a method leads the user to new places. It is still dependent upon his will to explore the paths suggested, but never leaves the user with the sense that he has seen everything—which would make the service valueless. Plus, since the user is encouraged to explore different viewpoints and different subjects, this method better equips the user to understand the true world around him.
I must point out that I respect and appreciate the services of both companies, and suggest you utilize them in your media pursuits. Ultimately, we are each responsible for balancing our own intellectual diets and pursuing positive trajectory in our learning habits.