To be fair to the Emperor, his past experience with Jedi had taught him that you can basically say whatever you want to them and they won't remember in five minutes.
My favorite is that Anakin's entire fall is predicated on, "I can save your wife, though." Then he gets back from betraying everyone he knows, murdering children, and getting maimed for the sake of this asinine plan to have Palpatine declare, "Woops, wife's dead and I can't help. Soooooorry!" This, somehow, does not cause Anakin to fly into a homicidal rage and rip the Emperor apart, or even reconsider the whole pledging fealty on the basis of a deal he gained nothing he was promised from.
I guess he just likes job security?