I like how one bad month for Nintendo basically boils down to "Nintendo is done" to most people.
For all we know, Wii Party could cause the Wii to get back to ridiculous numbers again. It's very difficult to come right out and say "OMG WII IS DEAD" from 1 bad month of sales.
Remember, Metroid was also the only major release of the month, and Metroid certainly doesn't sell systems as well as Wii Party and Donkey Kong have the potential to do.
3rd party sales are also not a problem for the Wii. Those still stay at the same level, if not higher than the other two systems. As far as I know, within the last 6 months, the Wii has actually sold the most third party titles, and pretty much always has since it was released.
I really think the lull in software, on top of Move's launch, caused a bad month for Nintendo. Overall, I see Nintendo having a strong, but somewhat weaker than last year holiday, with Wii Party and DK as front running system sellers. They could even pull a surprise NOA release of Super Mario All Stars and the red Wii, which will sell some Wiis.