When libgsf is "./configure --with-gio --with-gnome-vfs" it emulates its gnome-vfs interface with help of gio. This makes the dependecy on gnome-vfs unecessary for libgsf when configured with gio (which the ebuild always does). Packages that uses the gnome-vfs wrapper may still depend on gnome-vfs-headers, but that should in those cases be fixed in their ebuilds. For reference the configure.in entry from libgsf which shows this: http://git.gnome.org/browse/libgsf/tree/configure.in?id=LIBGSF_1_14_19#n424
I always wondered if there was something using the gnome-vfs part.
+ 13 Jan 2011; Pacho Ramos <pacho@gentoo.org> -libgsf-1.14.15.ebuild, + libgsf-1.14.19.ebuild: + gnome-vfs is not really required as explained in bug #351521 by Xake and + confirmed looking at upstream bug #593480. Remove old.