Some of the cheaper petrol might not be as well refined and is course in comparison to the premium stuff. As cars get more sifisticated it is easier for them to break down due to petrol problems. A friend of mine wont use the cheaper supermarket stuff as he notices a reduction in performance the same if he fills with petrol from a Jet garage.
These were that a refinery had taken "too wide a cut" with the crude oil allowing other products to mix with the gasoline.
Supermarket cheap stuff
An octane enhancer might not have been added to gasoline which needed one; sporty models goosed
or perhaps a biofuel like bioethanol was put into cars which were not designed to run on them.
Err that implies the motorist is somewhat scatterbrained which considering repair costs dosnt sound like something they would do.
The other answer could be a govenment conspiricy to keep cars of the road.
