A couple of spec's ago (SL, maybe?) Mobil posted on their web site that their bulk SL oil was lower spec than their cheapest bottled oil (Clean 5000 if memory serves). It met spec, but stayed in spec a shorter time in service.
I give Mobil credit for posting the truth. I'm sure that others do the same but keep it quiet. Maybe 3000 mile oil drain intervals are wise for that quality oil. None of this is considering the bulk tank that isn't kept scrupulously clean inside, and never filled with "psst...hey buddy, wann'a buy a truck load of cheap oil?"