Give it a month or two...
In a very short amount of time the x-box 360 will start releasing their new Holidays' content, dramatically increasing their sales of the 360 console. For example, I have not purchased one of the 'next-gen' consoles, but I plan to shortly, and when I do it will most likely be the 360, primarily due to the depth of the games currently, and soon to be, released. Nintendo's sales will jump once again once Mario Galaxy comes out, but their other games practically have 'ages 7-11' stamped on their front.
The fact remains that while there has been a surge of sales for the Wii, there will soon be another surge of sales for the 360 and, eventually for the PS3. The only real problem with any of these things is that they promise the world and end up falling short, very short of their marks.
But, in defense of Nintendo, they probably have the two best devices that do not market the casual or even hard-core gamer crowds, the Wii and the DS. These devices are quickly finding their way into the hands of the distinctly non-gamer crowds (e.g. my parents, my father enjoys the NYTimes Crosswords), a massively untapped market. I would probably relate it to Apple's recent meteoric rise, primarily due to the iPod, and its ease of use. The best description of what Apple, and now Nintendo, is doing is saying, "You don't have to be an expert to own and operate a computer, just try one of ours and see."
The main thing that will keep Nintendo on top is the parents that don't really have to worry about their kids getting their hands on anything horrendously violent, they feel they can let their 12 yr old play unsupervised for some time, plus purchase a couple of games that they can play (or at the very least comprehend without a step-by-step guide) with their kid. Their decisions will influence what the kid gets at Christmas, and therefore influence the overall sales of both the 360 and the Wii.
I'm afraid the PS3 is in for a rocky road in the upcoming years, being largely ignored. I just hope that Sony doesn't do something stupid and write it off as a huge failure. The best thing they can do is skip the mention of incredible graphics and such and start importing a ton of games that may be weak graphically, but are enjoyable enough with that one flaw.