Thanks all for your great responses, it does make much more sense now. Together, they make the picture complete: manufacturing, design, optimization.
As a comparison, I looked at the current Nikon lens lineup and they still sell both an f1.4 50mm and an f1.8 one. The f1.4 closes until f16, while the f1.8 can close to f22. Pentax also sell an f2.0 - f1.4 pair of 50mm primes, although both can close to f22. The desing also is different between the two (5g5e for 2.0; 6g7e for 1.4).
So I guess even 30 years later, those differences matter to some people!