I've spent half a day looking for the answer to my question,but it seems like I've gotten into Online Uru so late that these questions are considered noobish now,so I apologize first of all. ^^;
Not really noobish, it's just most of us got used to those various versions of Uru, and many here experienced the development of MOUL and then of what you can now see on DI - those many many changes were added gradually, but for someone new, it must be a huge pile of information and confusion
When MOUL started, it basically had the content of Until Uru. To D'ni mainly brought Uru Live Prime content to the offline game, so that content was available, but POTS was missing. Er'cana and Ahnonay were added in the mean time, but they are slightly different than in POTS, and the rest of the "Watcher's Path" is missing. The Watcher's Pub was added as Great Tree Pub in a modified version, Myst was made accessible through K'veer (if I remember correctly?), so MOUL now has almost all the content POTS had, but in a slightly different fashion. And of course, it has the new ages - the Pods, The Eders, Jalak, Minkata, and the new K'veer that's actually taken from Myst V.
DI is a wild mixture trying to give you both the POTS-version of the content, with the Path of the Shell story, and the MOUL additions - which is why some ages appear several times, and some places have to be reached differently. But all of the new ages are available and fully playable.
Usually this is referred to as the Offline KI "version" of Uru, because if you install the Offline KI locally, you will get the same content. For some more information, see
http://alcugs.almlys.org/Offline-KI/Features