If a virtual component is a part inside an assembly with apparently no external file, why does SW have an external file reference which can be lost?

example:  I renamed my assembly but the virtual component still referenced the old filename. If it's virtual inside an assembly should it not always reference the assembly it's in? I would have thought that until it has been save as an external file the assmebly name should not matter. Was not one of the ideas of virtual components to enable changes without all the external file reference problems, then when ready to put into production save all virtual parts with correct names?