There is no doubt the oils are better,but so are the ignition,induction,and exhaust systems. Modern engines mostly have overhead cams,aluminum blocks to dissipate heat,and computer-controlled everything.
When you add that all together,especially the computer controlled fuel,timing,and exhaust,it really makes a difference.
Seems to be the only "weak" link in modern engines is the timing belt. If you can call replacing a timing belt ever 80k or so miles a weakness. I have friends with commercial garages,and replacing timing belts seems to be a large part of their business. It's not unusual to see cars in for repair at their shops that have over 300k miles on them,and still going strong mechanically.
I also suspect they are balanced better than SOME of the old engines,although flathead Ford V-8's seemed to be balanced about as close as it is possible to balance one.