This, like the possible "parenthood" of Anakin are definitely left up for interpretation. However, I agree that Ian played this so that you'd think Palpatine was the killer. That said, some earlier objections were raised about why the Jedi would keep this from Anakin, if the Jedi didn't know the Sith were around at that time or know the story. Overanalysis at its finest. Palpatine is using all types of deceit throughout this movie to lure Anakin to the Dark Side and pit him against the Jedi. The Jedi aren't hiding anything from him. They're actually quite upfront about their motives for putting him on the council. "Lies, deceit, creating mistrust" are the ways of the Sith.

For that matter, it's possible the story of Darth Plagueis creating life can be a total B.S. story Palpatine is throwing at Anakin, knowing Anakin's desire to keep those dear to him from dying. His mother (whom he told the story to) and now Padme, to whom he now senses Anakin's connection.