See also my review of the entire book on GoodReads.
I would agree that each media is specific – books and films are different. And when books are adapted into films – the material changes. But this quote also points out something astute – more and more often, especially in pop culture, an icon or character is a multi-media experience. Batman started in the comics in 1939, and still exists in the comics – but there have been multiple series of films, live action television series, multiple animated television series, animated films, video games, etc. Each of those different presentations, will have different requirements. Films, for example, need a definite ending – both individually and in a series or trilogy. But comics, and television shows, by their very nature are on-going. Video games need interactivity and multiple possible storylines.