The cheapest grade of fuel works just as well as the spendy stuff. There are only a few auto's out there that require higher grades, and to all of the people that own them it isn't that big of a deal to pay a little more. A drop in the bucket.
This isn't exactly 100% correct. There are a number of cars that really need the extra detergents that are available in some brands of gasoline (I'm not talking about octane levels). This has been a problem throughout the oil industry. Over the years, the amount of detergents in the blend has been dropping. I believe these are known as "Top Tier" gasoline suppliers. The reason that this becomes important is because of problems with the EGR system design in some engines, you can wind up with some very serious "sludging" problems. Early and mid 90's Toyota Camrys are a really great example of this. There are LOTS of examples of Camrys needing their engines replaced with less than 70,000 miles due to oil starvation.
Mark