You are correct that engineering and materials are constantly improving year after year.
On the other hand I am diving a ScubraPro Mk25 1st stage from 2003 that is nearly identical to another Mk25 I got in 2019. Both use the same service kit and are completely interchangeable. I suppose I could spend a lot of money on a newer Titanium model, but otherwise this design will likely still be sold nearly unchanged in another 20 years.
You said "nearly identical" this is probably because there have been some changes in parts over time due to availability of better material, better engineering, better manufacturing, etc.. One such case is the change in the S600 second stage, piston, etc.
The engineering and materials improvements you are referring to that are brought about in other markets, space program for example, eventually trickle down to other industries even those that seemingly have absolutely nothing to do with the originating industry. One example is the space program for sure. Long time ago I was part of a team that did engineering investigative work on how to apply a technology used on the space shuttle for terrestrial application that had no direct relationship to the space program.
Scubapro is known to continue to improve its regulators incrementally even years or decades after their introduction to the market. Some of these upgrades are offered for free to owners of older makes of the same model and some other upgrades customers have to pay for these upgrades. Atomic does the same thing. (AL does it also but it slaps a new logo and name on the regulator and calls it a new regulator
