Sarah sighed and said "I wish Biff worshiped me." As soon as she said it, she felt an odd tingling sensation flow through her. And unknown to her (as of yet), her wish was granted.
But Jon was wrong about one thing, when he made his wish for someone (in this case, Sarah McMillan) to have their wish granted. He assumed that the wish would have none of the limitations that wishes made with the stone had. But that wasn't necessarily true. Though, his assumption that his memories wouldn't change was correct. Because of the way he made the wish, he would have to notice the changes (in the wish, he stated that at first he wouldn't like what was wished, but after a week, he would). So his memories would at least stay the same, even if everyone else's didn't.
