Web Directorys are build and managed by human beings. You have to submit your listing manually to the directory which is much more sumptuous and time-consuming than a simple search engine submission. Nevertheless the meaning of directory-listings should not be underestimated. The benefits of the generated links are very precious and will boost your ranking and the traffic which is generated by those listings.
You will notice a trafic and sales increase when google found a link to your site at http://dmoz.org.