The list is an aggregate, and most people probably would only have an interest in a couple of those. It's probably skewed towards new books, too; the sales for things like fad diet books probably drop off quite quickly. Long-term sales might be more interesting, as well. (Speaking as somebody who worked in a public library for about six years, people are more likely to grab something intriguing on a whim if it's free.)
Also, there is no "average" person, just aspects that pop up more frequently when you combine characteristics of lots of people. Individual people, even people you might at a first glance consider shockingly mundane, have their interesting sides. People viewed as a group are like stones that have had most of their interesting scratches and edges polished off.
I wonder if the general stats for the books hold in other countries. It would be interesting to see if France or Germany had the apparent weight loss and self-help level of interest that we have.
Also, there is no "average" person, just aspects that pop up more frequently when you combine characteristics of lots of people. Individual people, even people you might at a first glance consider shockingly mundane, have their interesting sides. People viewed as a group are like stones that have had most of their interesting scratches and edges polished off.