There are two reasons why I didn't address OODBMSes
And you're perfectly right. For now OODBMSes are still more than ever small exotic things compared to mastodontic RDBMSes (commercial rules applies...).
In fact, I always found RDBMSes complex and difficult stuff, even a bit archaic (the gap from sequential-indexed files is not so wide).
Here's some interesting reference about OODBMSes:
My two favorites:
If the only tool you have is a hammer, you will see every problem as a nail. --Abraham Maslow
Bien faire, et le faire savoir...