I feel the author is writing about the ability of Amazon to use it's size to create a hostile environment for smaller companies. If you take a large enough portion of quality books and offer the author cash to make them exclusive then you'll shut down competition.

There is obviously a grey area here. I don't know how much Amazon is in the business of creating books (i.e. hiring authors to write them).

The main difference is see between this and Netflix exclusives is that Netflix takes an active have in making their own content (it's a Netflix movie, not a X director movie on Netflix), they have competition in the marketplace and the financial dynamics of movies is different from books.