You had to ask... :)

On EL6, %attr is required for every %ghost file.

On Fedora 19, %attr is optional for %ghost files.  However....
* if the file is marked as %config, it doesn't have to exist during rpmbuild (after all, it's a ghost)
* if it's marked as a %dir, it doesn't have to exist ([fixed in F18](https://bugzilla.redhat.com/show_bug.cgi?id=839656))
* if it's marked only as %ghost and has 0777 attributes (it's a symlink), then rpm seems to assume it's a directory, but strangely requires that it's present in the buildroot (seems this is a variant of the above BZ, which I hit while testing this)

So it seems you need to leave out attrs to get it to build on F19 (else it fails trying to find the ghost), but you need them on EL6 all the time.