Saying that if two different oils meet the same specs and certifications then they will perform exactly the same with the same results is like saying that if car A gets the same NHTSA or IIHS crash ratings as car B then both will perform the same in a crash. The differences might not be huge but there will be differences. I think it comes down to whether someone feels comfortable with using any oil that meets the minimum specs or if they want to use the very best oil they can easily obtain that might surpass the minimum standards.
I am sure there are differences since specs are a min requirement, and some exceed specs while others barely meet them.
The problem is that people use their feelings or anecdotal evidence to suggest that one is better than another. Nobody is going to be able to get to the bottom of it