I don't think it is about detergents so much as it is about octane, which relates to how well a fuel resists detonation. The higher the octane, the less likely the fuel will detonate. Octane requirements for a particular motor depend on ignition timing, compression ratio, and I don't know what else. If you put regular gas in a modern car designed for high-test, performance will suffer because the lower octane will cause detonation, the knock sensors will pick up the detonation way before your ear does, and the computer will retard ignition timing. In older cars, using regular gas in a high-test car will shorten engine life because there are no knock sensors and no computer to retard the timing to prevent detonation.
I'm no expert, but that's my story and I'm sticking to it.