All Links Matter
The Myth about SEO that the page rank is every thing conceives a wrong story. All that matters is the Link popularity of a site that is the number of links that points to your websites from other sites. The story behind this can be falsified by the fact that the PR of a page can be changed in an update of Google.
The links exchange then becomes a tedious job when the webmaster believes the Myth, as the Myth forces webmasters not to exchange the links, until and unless the webmaster personally knows you. However in practical it in not like that, that the site with PR 0 will not get the traffic and the site with PR 5 or more will be getting traffic.
The fact behind the marketing via SEO is that the unique link pointing towards the site is whole solely considered by the search engines and thus the unique links from other sites are responsible for the marketing of your sites.
The relevancy of a page weighs matters a lot for the purpose, but to overcome the requirement of relevant links you may require to collect a huge number of links pointing at your website.
The Directories exists there, which are helpful in collecting the links, where as the links at directories are also considered and the traffic at the directory is targeted towards the sites when user searches for some specific topic.
These directories are a great resource for search engines as they help categorize the Internet - that's why directories will always be important on the Web, and being a part of directory always pays you back.