I think this is just one of many things that we once had that Amazon has taken away. I'm not sure why. Older non-KF8 files still can be displayed in multiple columns on K4PC.
Newer Kindles no longer have the progress bar across the bottom of the screen to show graphically where you are in the book as well as where the next section is located. I miss this feature more than any others that have gone away.
Currently: Kindle Touch, iPhone 5, and iPad 3.