Hi PapaMike,
While all foam will soften to some degree over time … latex is the most durable of all the foam materials and will soften less than other types of foam.
The softening sensation that BigWind was referring is most likely related to choosing a mattress that was “on the edge” of being too soft and would almost certainly be a comfort issue rather than an issue that was related to any unusual softening of the latex itself (see the last part of my comments here).
The firmness around the lumbar zone they are referring to is because of supportive properties of latex itself because of it’s inherent compression modulus (the rate that a material becomes firmer with deeper compression) and not from any specific zoning (see post #7 here)
Phoenix