Was there still some bad blood between Denise Crosby and Rick Berman, or did the producers of the film simply forget? I would think that it would have made more sense if it was Sela who had manipulated Shinzon into doing what he did for her own benefit. Had Shinzon succeeded, Sela's revenge against Picard would have been that much sweeter. And if Shinzon failed, Sela could claim deniability. Of course, there could have been an opportunity for Yar to return, but, alas...