As distributions evolve, developers make changes. Sometimes, the developers behind a distribution choose to drop services. Sometimes the service that you're most comfortable with was never built for your distribution. Sometimes people convert from distributions or allied systems, such as HP-UX or Sun Solaris, where different services are available. In any of these situations, you'll have to look beyond the distribution repositories to install the service you want.
For example, while the WU-FTP server is the default on Sun Solaris 10, it has been dropped from Red Hat and Fedora distributions. It isn't even available in the Fedora Extras repository. Nevertheless, if a company is converting from Solaris to Red Hat Linux, the administrators would naturally look to install WU-FTP on Red Hat Enterprise Linux. (In my opinion, that would be a mistake, but we'll explore that issue in more detail in this annoyance.)
The developers behind your favorite service may have built what you want for your distribution. If they have, that is your best option, as it ensures that:
Configuration files are installed in appropriate locations.
The package becomes part of your database.
The developers are motivated to help you if there are distribution-specific problems.
If the developers behind a service have built their software, and have customized a package for a specific distribution, they have an interest in making ...