The DVD images carry the complete distribution, but not the metadata used by the update tools - the repodata directory (I believe the headers dir is not needed for yum 2.1) Mirrors that are short on space, and other places making a local repository, may wish to loopback mount the DVD ISO, copy the DVD or or use a DVD as a local repo; however this repo is incomplete without the metadata. Adding metadata to the DVD ISO would make this use of the DVD images possible without nasty symlink magic.
*** This bug has been marked as a duplicate of 139077 ***
Changed to 'CLOSED' state since 'RESOLVED' has been deprecated.