Overall, since this will also be on consoles as well as PC, Im willing to bet that there will be DLC in the future for it, so I highly doubt there will be that many quests with the main release of the game. But after certain DLCs are released there may be up around that many
One of the interviewers who got to play the game noticed a DLC option or space on the main menu, and when he mentioned it, the producer covered it with her hand, saying they weren't discussing that at the moment. So I'd say DLC at some point in the future is a certainty.
Some of the unmarked quests in Fallout 3 are better then alot of Oblivions side guests.

Absolutely. A lot of the quests in Oblivion were in the item fetch mold. Such as retrieve 10 magic stones, or kill three bears and bring me their teeth, etc. Not hard to implement, but not exactly anything amazing either. While in FO3 we had unmarked quests like "A Nice Day for a Right Wedding", where you played match maker for a couple, which involved quite a lot of work for a successful outcome, and actual sidequests like "Agatha's Song" which while still a fetch quest, had an amazing story, sent you all over the wasteland and into Vault-Tec HQ, and then into a Vault with its own story, and rewarded you with a new radio station. Not to mention quests like "Stealing Independence", which was much more detailed and involving than the majority of Oblivion's quests.
If all of Oblivion's 200+ quests where like the "Whodunit?" Dark Brotherhood quest, that would be one thing. But can you really call something a quest when it involves returning an NPCs stolen potatoes from an ogre corpse just down the road? An ogre that is already dead?