Featured pictures exist on many projects and, the process of featuring a picture is different on each project. When a picture is featured, it adds real value to the picture. This value is in the exposure it gets on the main page of the project and when it is featured on Commons, it becomes eligible for the "picture of the year" election.
The featured picture of the English Wikipedia is in some ways the more relevant one. As it is featured on the Main page it is seen by many people. Wikipedia is an encyclopaedia, there is a need for the pictures to have an encyclopaedic relevance as well.
This picture of the Oklahoma bombing is currently a "Featured Picture Candidate" on the English Wikipedia. It is the leading picture on the article on the Oklahoma City bombing and it is unlikely to feature because of the existing quality requirements for a picture. It is likely that we could get a truly high quality picture from the people at DefenseImagery.mil.
It is probably good to have these high requirements for a featured picture. The best arguments is that a "featured picture" at the English Wikipedia makes a picture relevant.