The backup selections list or more correctly the Catalogue information is stored on the server within the database, and allows you to quickly restore the information you've backed up. If this information was stored on the tapes it would take up a LOT of space on them, as they can grow quite large.
If your media server did indeed blow up it would not however be the end of the world, as you would instead simply need to setup a new backup system, and then before restoring the information from the tapes you would first need to catalogue the tapes, which would read the entire contents of the tape, and re-create the catalogue information which you had lost. This can take some time, which is why you have the catalogues stored on the server normally.
