cockney steve, you are thinking about it from a consumer contract view point. That is that the consumer has little power in the creation of the contract, and as such implied terms are added to the contract by the state or common law in order to protect the weaker party. As such terms are added to the contract implicitly including fit for purpose, as displayed etc. However these terms are limit in extent, for example it must be in line with the quality of the product's value and life span. Additionally these terms are normally only included in contact to small value purchases or household goods.
For large commercial contracts it is very different. The parties are both considered able parties and as such have a duty to look after their own interests in the creation of the contract. For this reason terms pertaining to the performance, timing, quality, and warranties of the products should be included by the parties to protect their interests. This also gives the parties much greater freedom, as they can decide what they are willing to pay for or contract. For this reason different airlines could have different terms and extent of these terms. However other basic terms are normally included by default including dealing in good faith.