Ray McDonald was arrested, but has not yet been charged. Due to the presumption of innocence afforded by our legal system, the 49ers are waiting for the legal process to run its course before acting. It would be unjust to impose a suspension before knowing if he is guilty of the act of which he is accused. As far as I know, McDonald has not yet admitted to any wrongdoing, whereas Rice admitted to the act and was caught on video.
IIRC,he took a diversion program to avoid prosecution.