But I think that's the point. In a book you don't "see" the visual effects, you just know that they happened.

When you watch a movie, your eyes and ears has to collect the information, and some part of your brain has to turn that into a log of events. You have to do a lot of work to do to keep up with whats going on.

When you are reading, you don't need to do all that work, the author has already decided what is important.

I think the two mediums aren't really comparable, they both just happen to be good ways to tell stories.