Nautilus has options for what to do when media devices are added.
How does Nautilus know what applications to make available in these drop-down menus?
How do applications plug themselves in to this mechanism?
Nautilus gets this infomation from the
As far as I understand it this is handled by the MIME, the same thing that handles what application opens which files. system (sorry I don't have the full details).
EDIT: DoR answered as I was typing. He nailed it.