Hi GP,
You’re right that different manufacturers will use different designs and methods and there is really no “normal” way to build a mattress because there are so many variations of design and construction that can be used successfully to match different mattresses to different people.
The most important part of choosing a mattress is to make sure that you do some careful and objective testing on a mattress so you are confident that it’s a good match for you in terms of PPP and to make some good comparisons with other mattresses based on the parts of your personal value equation that are most important to you. There are certainly no “weak links” in the design in terms of quality or durability.
Only you can know which mattress is the best “match” for you based on your personal testing or experience (nobody else can feel what you feel on a mattress) but if the mattress you have is too firm for you then I would certainly talk to them about the options you have that may work better for you in terms of PPP. I would also try to spend about a month or so (if possible) on any new mattress you purchase so that it has a chance to break in and you have the chance to adjust to a new sleeping surface (see post #2 here).
Phoenix