My 1st wife at one time was the tanker dispatcher for a small local oil/gas distributor, back in the late 80's. She said the same thing back as mentioned above, that all the "brands" are really the same gas stock from the refineries and some of the major brands have an additive package the lesser known brands don't have.
Based on that going back to the 80s and what is said above, I'd certainly believe it. Although, I do try to buy well known brands of gas more often than the lesser known brands.
Here in Wisconsin and Iowa, the Kwik-Trip brand of convenience stores are huge and in almost any city big enough to have a store. For years their have advertised "top tier garauntee", they insure you'll never have a "fuel related engine problem" using Kwik-Trip gas. Interesting marketing ploy. For one, if you did have a problem, you'd have to prove it was their gas, and you'd have to prove their gas specifically caused the problem. Well, if they're getting the gas from the same stock as everyone else, how could you ever prove it was their specific fuel?
That said, in over 210,000 miles on both of my BMWs I have never had a fuel related engine problem (knock on wood, or noggin, same thing)