Right, you keep saying "I don't believe", while given no justification for that belief. 
Plenty of these engines have failed over the years. It is essentially impossible to accurately point to the causes for the failure, let alone catalog that data across all the failures. Absence of evidence isn't evidence of absence.
Yes, there is still an oil film on everything after oil has "drained back" in an engine without a check valve. That is generally good enough to prevent most wear during low speed, low load (like cranking). But once the engine fires, loads and speeds skyrocket, and a film is not enough. You need oil pressure to keep components separated, and prevent wear. If an oil film is enough, than explain why a loss of oil pressure in a running engine and cause failure in a matter of seconds or minutes. If you can reduce no oil pressure operation time by a couple of seconds on every start, the cumulative effect across 10,000+ starts is going to add up to something. I don't have that data, but it seems like a logical hypothesis to me.