As a car guy myself I get where you are coming from however I believe the difference is that in the car world, you are dealing with "man vs nature" in that we are trying to go faster or stop faster etc which is simply fighting gravity in the end. There is always a way to go faster (or fight gravity), we just haven't figured it out (yet), and thats with any car/vehicle. In audio, and this is general, the reference is a live performance let's say. If a speaker can reproduce that exactly, that is the "end game". No where to go from there. We spend alot on trying to get as close as possible to that live performance(or the exact recording) we may be 99% there and spend multi thousands $ to get to maybe 99.3%. With cars, say in 1960, an 8.84 second quarter mile was the NHRA record. Today, NHRA guys do it under 4 seconds. What will it be in another 30 years?
Summing up, if you look at the last century vehicles have gone from model a's to space shuttles and still growing. Speakers in their general form have not changed much.....