Why only 5 lugs on such a heavy vehicle?

[1990HR]

Doing a brake job on my 1990 HR and had to get a 4' cheater bar to break the lugs loose.
Threads are fine, no rust but someone over tightened them. (Previous owner or shop)
Looking at the service manual, it says 120 ft/lbs.
Why only 5 lugs on the front and tag axle?
My pickup has 6 lugs and weighs 1/3 the weight.
Anyone know what the engineers thought in 1990 compared to what they think is right now for lug nuts?

[tmsnyder]

Only 5 lugs needed on the RV b/c steel is strong, and the diameter of the bolts is larger too.  It's designed to do what it needs to do.

There's more lugs on your pickup for marketing purposes, that's all.  Personally I wouldn't get caught dead driving a pickup with 5 lugs.  That's so 1980s.  6 is marginal.  That's why my k1500 suburban is an 8 lug. If they came with one that had 10 I'd buy it.   

There's a recent article in this forum of a member who's lugs broke off after they had been over tightened so something to keep an eye on. Thanks for posting the torque spec on the HR lugs,  good to know.

[Rickf1985]

While an RV is big it is not really all that heavy by truck standards. 12 -14 thousand l pounds is really not much weight in truck terms. My 98 Dodge dually pickup weighs almost 8,000 lbs empty and 12,000 plus with my slide in camper on it. A school bus for example will start at 26,000. Those P30 chassis were grossly overloaded for many, many years in commercial use with no problems and they are actually a ten bolt wheel but the most weight is in the rear so they only use five bolts in the front where the weight is less.