6% for 40 years is a bit over 10x (not 8%)
The math is (1 + %) ^ 40 == 10 which means if you put in 6% you get 1.06 ^ 40 == 10.28 thus 40 years at 6% will get you 10.28 times the number.
Now, add in the extras (anti-lock breaks, water cooled engine, airbags, air conditioning, power windows, etc) and you seem to have a much better/nicer/safer car for around the same price given your 6% number.
Note that inflation has been all over the map over the last 40 years. Since time value of money can not trivially be reduced to averages, it is not clear what the right number is, but if you look at the 3.5% number I have seen as the effective average over the last 40 years we see that you get only a 4x multiple rather than the 10x. This seems much closer to reasonable considering the significant differences between the VW bug from 1968 (a very simple device) to the one from 2008 (a rather complex and sophisticated device).