BuddyPress.org

What does your link to the ‘community’ bp look like? Just: http://wikiroma.it? If that’s the case then the .htaccess rule you specified:

DirectoryIndex home.php index.php

Takes over and loads home.php like you told it to. If index.php is not specified explicitly with http://wikiroma.it/index.php then you’ll get home.php.