^The link I provided was just an example of how stems are tested.

Torque and lever arms are sometimes difficult to explain. Picture it this way:
The handlebar is two wrenches, connected at their jaws. Their jaws are on a nut in the middle. You can use both hands to twist the nut.
The jaws and the nut are the focus of all the torque. The nut is analogous to the center of the bar, the stem, and steerer tube head. That's where all the effort is concentrated, and why the industry made all the changes I referred to earlier.