To start with, those familiar with TES: Arena will know that the same Emperor they saved in the main quest of Arena is the one we see in Oblivion. Uriel Septim VII spent an extended period of time in Dagon's Deadlands, yet he was not killed. He must have made a deal with Mehrunes Dagon.
At the beginning of Oblivion, the Emperor knows he is going to die. He knows this because he planned it. He tells you this under the guise that he "sees more than lesser men" by pretending that he recognizes you, when in reality he realized your unfortunate presence in the off-limits cell would mean you'd have to come with them. He decided then to use you as a pawn in his plan. If he was truly so "psychic" and if he relied on the stars, why then could he not figure out your own birthsign?
When the time came for him to die--he already let the Mythic Dawn in to kill his two sons, as he knew their exact locations--he gave you the Amulet of Kings. He told you then to find Jauffre, because he knew Jauffre knew the location of his last son, Martin, whereas he had only checked in on him from time to time, and perhaps it had been a long time since his last check-in since he's been so busy plotting the destruction of Tamriel. He intentionally gave
you the Amulet of Kings and told
you to find Jauffre, because he knew Baurus would take it from his corpse and put it in good hands, whereas you knew very little about it, and you might be more careless and lose it or die with it, and even if you didn't, with the coming Oblivion Crisis, the odds of you surviving and the Amulet of Kings remaining safe was practically non-existent. The later attack on Weynon Priory was the result of Uriel's information, as he knew exactly where it would be because he told you to give it to Jauffre.
It was a roll of the dice, however, Uriel never expected you to be so competent, never expected the Blades to be so adamant with a dead Emperor, and never expected a simple priest to survive a full-scale invasion from Oblivion.
See, you can come to any conclusion if you look hard enough for it.