Hi delrose,
The specs in Ausralia appear to be a little different from some of their mattresses in North America. You can see some of my thoughts about Technogel here and some of the North American specs in the middle attachment in post #3 here and in post #2 here. There is also more about Technogel in Europe in this thread and a forum search on Technogel (you can just click this) will bring up more comments and feedback about them as well.
You can read more about the factors that affect durability and the useful life of a mattress in post #4 here. While it’s true that deeper layers will be less stressed and the layers above them will absorb more of the stress from sleeping on the mattress (a mattress will tend to soften and break down from the top down) … I also think that these are clearly on the low side … especially for a mattress in this price range and the comfort layers would seem to be a weak link in the mattress in terms of the comfort life of the mattress. An inch or so of lower quality materials is usually fine but once you get into the range of about 2" or more it can be a weak link in the mattress and this has 3.2" of lower density materials in the upper layers (assuming all of these are memory foam and not polyfoam). I also don’t know why they would use 1.5 lb density base foam in a premium mattress (outside of cost savings of course) although this would be less of an issue with durability unless someone was in a heavier weight range.
Phoenix