Dave Johnson on open web technologies, social software and Java
This point is probably better stated by saying Roller requires a JDBC accessible relational database and CocoBlog does not. There are advantages and disadvantages of using a JDBC database to store blog entries, bookmarks, newsfeed info, etc. of course.
For example, because Roller uses a possibly-remote JDBC database for persistance it is easy to distribute Roller accross multiple VMs. That is important when you need to distribute the load on those high traffic days when you have nearly 10 hits occuring in a 24 hour period... Ok, so maybe it is not that important.