detergents in petrol

my car manual says that i need to make sure i use petrol which doesn't have detergents in it. on close examination all fuels now contains 'engine cleaning detergents' even asda shite petrol.

now why this stupid rise in adding detergents to petrol? i don't remember engines getting their insides all dirty before. i thought engines were meant to be a bit dirty (like christina aguilera).

could it be that instead of selling us the product we want at the lowest price they are 'adding value' by diluting the product with cheap shit detergents which degrade the fuel economy of the car etc.

wankers