Would be trivial to move to hard links, but for all the reasons outlined below symlinks seem to make the most sense right now. Agreed that if you delete the base file, all the symlinks break is not optimal. Would appreciate help, fork it, and make it better.
Hardlinks cannot link across partitions. Symlinks can. Therefore symlinks always work, so it is easier to use.
Symlinks don't work on all filesystems, so don't always work.
Hardlinks don't always work well with tools; IIRC, I've seen backup tools support symlinks but not hardlinks.
Also most modern systems don't support hardlinks on directories.