One thing that does vary from person to person is that some people hear the words in their head while reading silently to themselves but others don’t (and some people do only sometimes)—see the old SDMB thread “Do you hear words in your head when you read?” for anecdotal evidence and discussion.
That may or may not be relevant to this thread, but I can’t help wondering if there’s a correlation between whether a person hears the words in their head when they read and how much they appreciate audiobooks. And, if there is, what sort of causation is involved.