In favour of Sony: PS3 reached its first real sweet spot recently, so it has more potential for sales boosts.
Against Nintendo: Wii was affordable since the beginning and already had several Mario games, so die-hard Mario minions should already have bought one and a new Mario game, despite selling an awful lot of copies as it will, won't move many more consoles than usual.
In favour of Nintendo: we're talking about Japan, so, if we aren't Japanese gamers, and with strong Japanese market analysis skills too, we cannot really tell very much for sure.