As long as the hardware sales stay this low in Japan, it is really completely irrelevant who gets beaten by whom. The question is which console has the potential to sell in the 50k range for some weeks in a row.
I actually see greater potential for the Wii since it has a more diverse lineup. On one hand, it has a couple of second-tier (sales-wise) RPG's coming which all should give hardware sales a small boost, especially since there were barely no RPG^s yet on the platform.
Also, the whole Monster-Hunter-followers probably don't own a Wii yet, so the release of those games should give the Wii hardware a huge boost. The same goes for Dragon Quest, but this game is still to far away.
Then there is Wii Sports Resorts, which could also raise Wii's hardware sales. It has to be seen though if the game will be bought primarily by the people that already own a Wii or if it will also cater a lot of new people.
Then there is still quite a number of genres that aren't really crowded on the Wii, regarding Japan I primarily think about fighters as a genre that could revive hardware sales.
The PS3 on the other hand doesn't seem to have so much potential. FFXIII will definitely give the console a great boost, but I don't see that much apart from that. Gran Tourismo will also increase hardware sales, but not by as much as some people expect I think since I see Sony fans and graphic whores as the primary audience for GT, and those groups already own a PS3.
So in my opinion, Nintendo doesn't need to care about the PS3. It has to care about low hardware sales however. The next three months should show where the Wii really stands though, since important games like Monster Hunter and Wii Sports Resort are launching during that period. If the Wii's sales will be declining sharply after those games are launched, Nintendo should definitely lower the price or do bundles or colours. If not, they're fine.