It sounds like Nintendo are gearing up for a frontal assault on the western market. Kind of makes sense at this time, really, as they are definitely very well prepared financially for such an endeavor. I think the strategy is about creating a clear distinction between "real games" and "apps", hence the importance of extra-high production values, high-end hardware and fantastic support from third parties. To put it in the words of Iwata from GDC, it is about creating a solid ecosystem where games are the main focus, rather than "something someone else makes"... or at least that's how Nintendo sees it.
Also, if you think about it, iphone and ipad games are currently still in more direct competition with other mobile platforms. There are a few ipad games that can connect to a TV, but it isn't common enough to be considered a "home console" competitor yet. However, this is something that can very easily change with the right push from Apple (i.e. streaming games to Apple TV, allowing third party controllers, or some other similar endeavor).
In that context, this move can be seen as a sort of "best defense is a good offense" tactic. I don't know if I speak for everybody on this, but from my experience the most compelling iphone and ipad features at the moment are ubiquitous online connectivity (mainly at home) via wifi, and simple apps occasionally. Or in other words, I think alot of people get most of their mileage out of browsing the web from bed and playing simple games on the toilet 
If this is the case, then this rumored "tablet controller" could offer just such an experience while in the home (feeding off the main console) and possibly even limited use outside (if Nintendo can get it to work as a general wifi device away from the console). This would then create direct competition with gaming on mobile devices, to the extent that they may end up being too occupied with the battle for their home territory to branch out as a serious competitor in the home console space. The killer-app that Nintendo could offer in this respect imo would be SMS texting* over the cellular network, or some simple way to transfer your phone contacts to an internet messaging service. If they could do that then I suspect some people would even consider having only the one device on them, occasionally.
(*The cost of service to the operator for text messaging is actually extremely cheap, as it relies on spare bandwidth between voice data to send the messages - this doesn't mean cell companies aren't aware of its high value, but, just saying...)
In addition, it also opens the door for many new ideas in gaming and entertainment, as you could take your controller with you to the outside world and gather data that can later be imported into games on the console (like sound clips, textures or even more complicated resources). Not to mention the extent to which it could further integrate gaming into the common life-style (like a continuation of the "pedometer coins" thing on the 3DS) and even become a more widespread social platform of sorts (for example: watching video clips from last night at the bar with the guys on your TV in animal crossing, or something
).
Still, it makes you wonder about the continued viability of the 3DS in such an environment. Perhaps Nintendo will announce it as an optional controller for the home console (even though it only has one analog stick...
).