Its probably his work truck, and when he has to pickup larger flat material from the hardware stores it is more convenient for him to keep smaller stuff in the rack, instead of having to shift everything around (tool box, cooler, etc.). Or it is his family car camping rig, and he/she likes having the extra rack for additional gear. As a trend, I am starting to see more over-bed style racks around here as well (like the one pictured).