Imagine a cargo ship, of the container variety. It is a big boat with an empty space in the middle; that empty space can be filled with containers. The shipping port has facilities to handle containers and load them onto the ship. The ship has facilities to secure the containers, track who owns them, where they are, and where they are going. As long as the containers match some basic specifications - shape, size, weight - only the shippers and receivers of the container care, or possibly even know, what is in it. The shipper probably packed the container in some way that made sense to him based on his knowledge of the product, so that it will arrive intact; the receiver expects to be able to unpack the container and put the contents to use. While that is the primary concern of the shipper and receiver, neither the port or the ship cares about any of that; they just move containers around, and maintain only enough information to ensure the containers get to their intended destination on time and undamaged. The shipper who packed the container doesn't care how it gets to its destination, only that it gets there on time and undamaged. The receiver doesn't care how it got to him, only that it arrives on time and undamaged. The content of a container is only of interest to the shipper and the receiver, and their interest in it is only linked by the nature of the content, not by how it was moved. If the shipper thinks it is necessary that the cargo ship be painted a certain color and have exactly 37 crew members and that the crew be experts in the manufacture and use of the shipper's product, every shipper will need to build and crew his own ships.
Imagine now the good ship SS Scraps. Its port is the Scraps Administration Program, which has facilities to load "containers" into its database cargo hold. The containers have specific contents, but the Scraps Administration Program does not care about the contents, as long as they are packaged correctly. The "shipper" - the person digitizing and marking up some artifact - knows that the contents are an image file and a block of XML-formatted metadata, and the structure and meaning of that data are of great importance to him. The only data Scraps needs to know the meaning of is the data that lets it track and organize the "containers", and this data is of no interest to the "shipper" or the "receiver", who can just assume it is being taken care of. Scraps neither knows nor cares about the internal structure or inherent meaning of the data; as long as it is packaged in a properly-formatted "container", Scraps will store it and deliver it to the "receiver" intact. What the "receiver" - usually a browser-based Web application - does with the data is of no interest to Scraps. Scraps (the Scraps "engine") does provide tools that the browser-based viewer can use to unload the container and present the contents to a user, but even in that role Scraps does not know or care about the data itself - the internal structure of the metadata (Dublin Core, METS, or anything else), what the image is a digital representation of, what any of it means to the creator or the viewer - none of this matters to Scraps. How SS Scraps stores the "containers", tracks them, and delivers them to the viewer should also be of no importance to the "shipper" or the "receiver" as long as the container's content (the meaning and context of the data) is delivered intact. If the "shipper" wants Scraps to be specifically tailored to his product, there will need to be one version of Scraps for every digitization project, which, while possible, is not practical.
This is why Scraps is being designed to be utterly indifferent to the nature of the data it is working with: the creators of the data can focus on marking up and organizing the data in a way that is meaningful for any particular artifact without needing to concern themselves with how the data is stored and maintained, and Scraps can focus on storing and maintaining the data without needing to know anything about the peculiarities of any particular artifact. Thus is order maintained to the benefit of all.