Well the graphic says “should”. 
Also the " two potential supplies to the light" isn’t really correct. In the graphic there is one supply to the light because the travelers only are run between the two 3-way switches.
The wording is very confusing. There is no way to “check for open neutrals” in switch boxes that only use manually operated 3-way switches (they might be there but will be open (not connected)). Nor were neutrals required in switch boxes prior to the 2011 NEC (Article 404.2 (c)). The physical assembly that is visible can be checked (cover plate, loose switch, etc.) and the operation of the switch.
“Should” implies an obligatory requirement. “Could” would be more appropriate since other set-ups would satisfy the requirement and listed exceptions.
My finished basement stairway has a separate single pole switch at each level illuminating separate light fixtures. I solved the inconvenience of not having a 3-way by installing wi-fi enabled devices.
The wiring diagram works on paper and would work in a lab setting, but of the 1/2 dozen or so ways I’ve seen 3-way circuits wired, I’ve never seen it this way.
The graphic shows a two-wire cable (Black and Red) between the 3-ways any cable with a black and red conductor would also have a white conductor. As you’ve stated the configuration will work but it not something that would see in the field.
Regarding “should”, there might be 3-way switches for a stairway but it’s not a code requirement.
Good point. Either the light turns on or it doesn’t. If it doesn’t, let an electrician “check for open neutrals”. Besides, according to the diagram, there is only one place the neutral is present and no inspector in their right mind would remove the light fixture to check for open neutrals.
It is IRC code requirement:
R303.7 Interior stairway illumination. Interior stairways
shall be provided with an artificial light source to illuminate
the landings and treads. The light source shall be capable of
illuminating treads and landings to levels of not less than 1
footcandle (11 lux) as measured at the center of treads and
landings. There shall be a wall switch at each floor level to
control the light source where the stairway has six or more
risers.
Exception: A switch is not required where remote,
central or automatic control of lighting is provided.
One could bicker that you could get around 3-way switches by providing separate illumination at the top and bottom of stairs but I never see this even in older homes.
My house was built in 1920…
3-way switches are not required, not even today.