In The Making of Revenge of the Sith p. 62 the Fourth Draft of the script has the dialoge of that scene as: PALPATINE: ...Unfortunately, he taught his apprentice everything he knew, then his apprentice killed him in his sleep. (smiles) Plagueis never saw it coming. It's ironic he could save others from death, but not himself. According to legend, it was a power his apprentice found no value in. So the ability to save loved ones was lost with Plagueis "the wise". Obviously the cut dialogue was information that was unnecessary for Anakin to know.