You'll probably will still have to download, install and configure the database you plan to use, anyway, if you plan on using MySQL or PostGres. That is a much more daunting task. For more commercial databases, you have to start by downloading and installing the client libraries. Compared to these tasks, installing DBI is easy.

Besides, DBI without any DBD::* drivers, is useless.

OTOH, perhaps it wouldn't be unreasonable if Activestate started to include both DBI and DBD::ODBC with ActivePerl for Windows. That'd let those people have immediate access to their MS Office databases.