Any game that announces add-ons or expansions literally days after initial release, is more likely doing so to refuel the media-hype machine so it continues working for them, because they see a rapid fall-off in new subscriptions.
D&D Online does not deserve subscription fees because NeverWinter Nights 2 will be a vastly superior alternative. In the end all you are doing in D&D Online is getting together with a small group of people and running pre-made modules which are no where near as complex, or compelling as those made possible by the NWN tools.
Furthermore, D&D Online does not allow for exploration or encounters outside of the canned little "adventures" (yawn). It is the ability to go-a-wandering, and get killed somewhere that no one can find you, which makes an MMO game "massive" in my book - not the number of idiots running around.
And finally, D&D Online is not an RPG.. because there is absolutely no reason to be "in-character". By that measure, a true MMORPG has yet to be made, but nevertheless, don't be sucked in by that non-existent aspect. All the people do in D&D Online is stand around in pubs pretending to attack eachother advertising their character type and level, or recruiting a type & level. Then it's back to the grind... YAY! (yawn).