Hi SleepDeprived,
Zoning uses the same principles regardless of the type of materials or components in a mattress and the information there would apply to any type of zoned mattress whether it was foam or innersprings.
The hips and pelvis are the heaviest part of the body so a firmer zone in the middle can help prevent them from sinking in too far (which is one of the main causes of lower back pain) and at the same time the comfort layers above a zoned support core need to be thick and soft enough relieve pressure in the hips. Having a firmer zone in the middle and a softer zone under the shoulders can also help the lighter and wider shoulders sink in more deeply (for side sleepers especially) to maintain good pressure relief and good upper body alignment. In many cases hips tend to need to be “stopped” from sinking in too far and shoulders tend to need to be “allowed” to sink in more deeply. Having said that … different people can have very different body types, weight distributions, sleeping positions, and preferences so a particular zoning pattern may work well for one person and not nearly as well for someone else.
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel”.
Phoenix