What Tango said.
If you have to purchase a separate service (e.g. luggage) then you expect the service to be provided and no contract can take away your rights.
Luggage goes missing; its a fact of life. But it cannot cost as much as £40 to deal with one item of luggage on a plane. So the airlines who insist on charging should invest some of that money in better contracts with their handling agents so the service is adequate for the price paid by the customer. I can see someone having a go at an airline one day.