Thunar currently shows only mounts that have a volume attached to them.
But there are cases in which there can be a mount with no volume.

For example network mount, or FTP mount etc.

I've implemented this functionality in my Thunar 1.4.0 (with Disconnect button) and it looks like it would make managing FTP connections with Thunar possible (listing all ftp connections and an ability to "Disconnect")

(thunar-shortcuts-model.c, thunar-shortcuts-view.c, thunar-icon-renderer.c, thunar-icon-renderer.h)