Exactly. the sith rule of two is the Ultimate survival of the fittest. you live only untill someone stronger comes to take your place. And, frighteningly enough, they WANT to be killed by their apprentice, becuase it strengthens the sith order in the long run.
This is just my personal beleif here, so bear with me, ok?
i see palpatines forsight as showing him Multiple different futures, becuase as yoda ssays " allways in motion is the future" and every time a choice is made, some of the pathways he sees are forever closed to him. Seeing the posibility of what CAN be, is much different from what WILL be. This forsight allows him to plan and adapt in ways we cannot even begin to fathom.
Looking at his death in ROTJ, Vader made his decision to embrace the man he was, and acted on it FASTER than Palpatine could react and adapt.
If vader had been on a distant world, and been fighting luke, and decided to turn back, and turn on his evil master, Palpatine would of had time to adapt and put a new plan in place.
He was So CERTIAN of his victory, that He started to get sloppy, he never even imagined that Vader would turn on him. He expected the son to kill The father ,and then Take his father's place.
He was wrong.