All preferences programs do expand any path to the real name, even Assigns. And yes, i hate it.
The reason, IIRC, is twofold.
1. If you Lock a path and then query that Lock for the path, the OS will give you the full path containing the volume name (I have a feeling some changes were made wrt this in OS4, but assigns will still be expanded)
2. You can't guarantee that the volume inserted in a device will stay the same, so using the volume name allows the OS to request the correct disk. (less of an issue these days, but historically essential)