Actually, modern oil has as much to do with extended life as do clearances and metallurgy. Even the old engines live longer with today's lubricants.
Oil pressure too. Used to be 10-15lbs but now it’s 40-50lbs. Tighter clearances have also allowed for the use of 5w20/30 as opposed to 10w30/40 which is less apt to sludge, especially as you say, with the newer formulations.
And before that, SAE 30/40 single viscosity with no detergents would sludge real quick.