If you delay the MQ long enough in MW, and keep increasing your reputation and level, the Tribunal Temple authorities will eventually get concerned enough about the Dagoth Ur problem to track you down and ask for your assistance. Other than that, it's an old evil that everyone's aware of in the backs of their minds, and knows that it will become important someday soon, but it really doesn't interfere much with daily life except for the annoying ash storms and the steadily increasing problem with Corprus beasts escaping the encircled Red Mountain containment area. The first actions of the MQ include suggestions about doing other things to improve your skills, and getting established in the world; there is no hurry, although you can certainly jump right into at least the first couple of missions with a half-way decent combat character.
With Oblivion, the MQ is "in your face" from the first few minutes, and putting it aside is akin to "letting the world go to hell", quite literally. Doing other things in the mean time is contrary to common sense.
OB would have been a lot better if the events of the MQ didn't trigger unless you followed some opening advice, or until you reached a certain level or faction rank, and accepted a call for help.
Agreed.
I will agree that Oblivion and Skyrim seem to be set in a time when all hell has already broken loose, and it definitely takes away from the relaxing nature it could otherwise have. You feel like you have no business doing guild quests when multitudes are dying and cities are being swallowed. My aimless travel along the Colovian Highlands was constantly interrupted by turbid skies and daedra pouring out of Oblivion gates. Mehrunes Dagon is depicted to be very much evil and very present in the world. Dagoth Ur's alignment was ambiguous at best by the time you were done. At least in Morrowind, if you avoided Ghostfence, you had little to worry about unless you went looking for trouble.
Morrowind definitely had the air that these problems had built up for centuries little by little from some obscure battle at Red Mountain. You believed for a while that the Tribunal protected the land, and that's wonderful considering that most other citizens of Morrowind felt that way, too. By the end you knew the world was wrought with corruption, whereas Oblivion's premise seems to be that although everyone was screwed up they came together for some holy crusade against the "evil" daedra.
I would love a purely sandbox TES RPG, though unlikely, since the epic story line has served them so well. I would love to dedicate my in-game time doing mundane things (am I weird?) and worried more about status and income and maintaining a family and reputation rather than being some big hero. But having that as an option is nice, too. They would probably just wind up spreading themselves too thin and creating some kind of abandoned TC monster. Although there is a sense of free form and doing mundane activities, all of these plot lines seem to converge at saving the world. All of the little extras are just a way to get what we need to be the big hero. (ie: You can't pay for training you might need to satisfy guild requirements to get the next quest unless you make gold by selling pelts, potions, etc. etc.)