Handwave: Talosian Chimerastatic Shock caused by the Oblivion crisis and subsequent Dracolytic event at the Temple of the One. In essence, the Cyrodiilic eco-cultural-subgradient solidified into a more stable, durable form as part of an autonomic knee-jerk response to space and time being so severely dikeied with. And nothing is more durable than time-honored clichés.
Concern: How was Mankar Camoran able to wear the Amulet of Kings? I though only the Dragonblooded/Septims were able to wear it.
Handwave: Anyone could actually wear the Amulet, but only those of the Septim blood could manipulate the clasp on its chain (which was enchanted by Zurin Arctus himself). This is why it slid off the neck of the Champion of Cyrodiil when he inevitable tried to wear it to get free drinks at the Feedbag. Mankar solved this problem by tying the ends of the chain together with twine.
Handwave Addendum: To be fair, though, it was Daedric twine.
Concern: Why doesn't the Bruma Mage's Guild ever stop burning?
Handwave: As a memorial to those who had fallen (and subsequently risen!) in the struggle against the necromancers, the Mage's Council converted the actual fire into a building-wide eternal flame to honor their sacrifice.
More to come! But please, contribute your own!