Yes, first party. As for SMG2, I can't verify that but I remember seeing stories at the time of S&P being the first with these new cases.
As for motive, does it matter? The cases are still better for the environment, so I don't care why they did it. As for the size, that has become the default standard for games and movies (except Sony, who decided to make weird sizes for PS3 and PSP cases). I suppose they could do what Sega did for Dreamcast and just use jewel cases.