When I read your original post, I mistakenly thought that you suggested that wide bodies were commonly used on short to medium-haul flights around the world, and that 99% of them would be replaced by single aisle jets if AS economics were applied in the real world.
Nah... I am aware that the usage is quite limited (and additionally it has gone down significantly during the last 10 - 15 years).
However, I find it fascinating that they are still used in many situations.
I guess the key to success is described in one of the threads I linked above (Japanese Domestic 747 - A Miracle?), from where I will quote:
"There are no meal service to speak of onboard many JAL/ANA domestic flights, only drinks service. So there are very few catering supplies to be loaded and unloaded. Also no food service means less cleaning to be done in the passenger cabin. Anyway cabin crew walks with a garbage bag towards tha last stages of a flight and do their best collect all the rubbish.
All that and the fact that very few passengers check in bags means very fast turnaround times of 35-40 minutes even for a 747 or 777."
and
"I would put it down to many factors but the main one would be the Japanese mentality.
The pax come in, know where their seat is put the small hand baggage in the compartment and sit down, fasten their seatbelt and are ready...all within a few minutes of getting on the aircraft!
I have seen this happen and when talking to cabin crew on other airlines they say that the Japanese passengers are a gem as they take so little time to board, there are no pax wanting to change seats, or sit in the wrong row, no complaints, no turning up late etc..."
"I was really impressed by their service and I think it has mostly to be explained with their mentality, they are so aimed at efficiency that you can really board 500 Japanese people in ten minutes, believe me."
That last stament would imply that boarding happens at a rate of 1 pax / 1.2 seconds, which to me is hard to believe.
But this type of flights exists in the US too (where the "Ordnung is das halbe Leben" saying would apply to a lesser extent in comparison to Japan...), as per the following threads:
However, by using the Aircraft evaluation tool for, say, IAD - ORD (chosen from one of the threads above), we can see (Y / standard seats / price @ 100%) the following margins for 100% load factor:
26% for 739ER BGW
-25% (!) for 762ER