I believe most of this was in the lore already. That something was coming at least, resulting from the destruction of the heart of Lorkhan in Morrowind, and some of the other things from the other games... Not that they're just making the entire thing up right now. I don't know the details exactly. Any lore buffs here?
The disenchantment of the Heart of Lorkhan in Morrowind paved the way for the Oblivion Crisis (the Heart was basically a mythic symbol that helped hold up the barriers between Oblivion and Mundus/Nirn). The Oblivion Crisis resulted in Martin shattering the Amulet of Kings, which broke an age-old agreement of sorts with Akatosh (aka Alduin to the Nords). I don't think the exact implications have been worked out, yet.
I'm not really a lore expert, but I don't think the Staff of Chaos (from Arena) and the Numidium (from Daggerfall) were known to be pre-cursors to anything before now. I also wasn't around to know if there was any lore to foreshadow the Oblivion Crisis from the disenchantment of the Heart of Lorkhan before then (though there were some clear clues in the dialog for Tribunal and Bloodmoon, they came afterward).