I noticed this yesterday and thought it was really interesting. Being that last year was the 60th anniversary of the Ten Most Wanted list, the FBI came out with a historical booklet available for viewing here:

http://www.fbi.gov/stats-services/publications/ten-most-wanted-fugitives-60th-anniversary-1950-2010

It basically contains everything you'd ever want to know about it. Pretty cool, I thought.