I see 2 things going on here... . Not that either one is better then the other, its just a differences in driving styles and locations.
#1
A Large bunch of people who drive Fast 70+ That don't seem to tow heavy. I define heavy as hauling 15K+ trailer, so GCVW would be 24,000 lbs and up on a regular basis, Defined as 60% or more of the time. That don't realize or know that the 3. 73 gear with the G56 is like a 4. 10 rear end in the old NV5600 and NV5500 trucks. They really need or could use a 7th gear or taller gearing. Mainly a people transport, that can haul the RV or boat on the weekend. If you need example look at the mega cab... .
I would also believe they live in a open country, and with little traffic.
#2
People who do haul heavy all the time, near or past 26,000 lbs GCVR, don't travel at 70+ all the time because its there work truck and more then likely should have a semi truck but because its a Dodge with great power and decent gearing gets the job done. Don't get me wrong there are times on long hauls they drive at 75+ but this is in open roads. I would also assume they might live in mountain areas, and with traffic.
I fall into the #2 category, Personally I tow at 26K about 80% of the time, and have been thinking of going to 19. 5 but the increase in tire height might really suck when starting out from a dead stop going up a hill. I live in Washington and we have plenty of hills with stop signs. Right now truck is stock, starting up a hill category the clutch will glue it self making the next shift hard, this has only happened 4 times in 45K miles mostly its the hills fault and driving really loaded. . IE Im using the truck for more then it was designed for, it works though and thats what matters to me. but taller tires or gearing would make my life harder while towing, especially from a start and stop point of view. And then there is stop and go traffic, honestly there isn't a lot of times I can go 70+ MPH without running into traffic a mile up the road, Im happy traffic going the speed limit.
Honestly my truck is a Work truck, not a toy or pleasure truck, I need it to to work , with as little time as possible in the shop, if I loose 2MPG then well I can live with that, its the cost of doing business.
Again I fall in #2 others fall in #1, there is no coerect answer for everyone, only the coerect answer for you.