Maybe build quality of the assembly, but definitely not the build quality of anything mechanical! Modern cars have ludicrously better reliability than anything from the 60's to 80's. A car not making it to 100k miles is a rare exception these days, even with somewhat abusive upkeep.
Every car I have ever owned (9 so far since 1975) went far beyond 100k miles, even my 1965 Mini van that I bought in 1975 for 65 GBP. But I agree that the newer cars were much more reliable.
Maybe build quality of the assembly, but definitely not the build quality of anything mechanical! Modern cars have ludicrously better reliability than anything from the 60's to 80's. A car not making it to 100k miles is a rare exception these days, even with somewhat abusive upkeep.