Guess nobody read the link on MotorTrend I posted at the beginning of this thread:
You can thank the federal government, at least in part, for the current fad. When Ford's extra-girthy, desert-running Raptor checked in at 86.3 inches wide back in 2010, the automaker was obligated to put them on the pickup—any passenger vehicle over 80 inches wide is subject to the same lighting regulations governing commercial vehicles. In addition to amber front identification lights, a set of three red lights must be installed on the rear of these vehicles. These vehicles also require clearance lamps at the corners that are similar to identification lights but called out separately in the regulations.
Here's the Legal Definition
Federal Motor Vehicle Safety Standard Number 108, (aka Title 49, Subtitle B, Chapter Five, Section 571.108 of the Code of Federal Regulations) lays out the legal details around vehicle lighting. Among the statutes you'll find this gem describing how the identification lamps should be placed on any vehicle 80 inches or wider: "On the front and rear—3 lamps, amber in front, red in rear, as close as practicable to the top of the vehicle, at the same height, and as close as practicable to the vertical centerline, with lamp centers spaced not less than 6 inches or more than 12 inches apart. Alternatively, the front lamps may be located as close as practicable to the top of the cab." In other words, the Raptor is wide enough to require the same lighting as big rigs and dump trucks.