There seems to be a very strong trend of the number of wheel lugs on cars and trucks increasing over time. For instance, many small cars in the 80s used 4 lugs, but have since switched to 5 (e.g., Honda Civic, Volkswagen Golf).
More stark examples can be seen in trucks. Consider the M35 series of trucks used by the US Army. The standard model weighs nearly 13,000 lbs empty, and is capable of carrying a load of around 5000 lbs. Its wheels use 6 lugs. (See top photo)
The latest version of the Ford F-150, a truck weighing about 4500 lbs with payloads in the 1500-3000 lb range, now has 6 lugs. (See center photo)
Meanwhile, a vehicle more comparable in weight and cargo specs to the M35 is the Ford F-550. It has a Gross Vehicle Weight Rating of 17,500-19,500 lb range. It uses 10 lugs per wheel. (See bottom photo)
So why the lug inflation? This answer states "To some extent, the number of bolt studs depends on the anticipated torque on the wheel." While it's true that engine output and braking power have increased over the years, have they really increased enough to merit a 66% increase in the number of lugs in this example?