I just found the following text in the developer guide, so the question is not valid, I guess. However the text that says "the key must be included in the URL" is incorrect, it should be part of the body.
For CREATE requests, for example, to add a new entry to either a table or an SQL view exposed by an OData service, you must specify an explicit key (not a generated key); the key must be included in the URL as part of the CREATE request. For UPDATE and DELETE requests, you do not need to specify the key explicitly (and if you do, it will be ignored); the key is already known, since it is essential to specify which entry in the table or SQL view must be modified with the UPDATE or DELETE request.