At first I just wanted to join in the main arguement but wowzers it's getting big so I guess I'll just stick with a few smaller basic points
I would say I partialy agree with you here, the DS's main purpose was to increase the level of interactivity for sure but it's interface not only brought in the touch screen but also a mic as well as dual screens (which is important for some genres) as opposed to the Wii which has the gyros in both controler pieces and the pointing sensor which are all based off the same motion premise (though a Mic may be coming soon).
However the thing that is often ignored about the DS is that it was still a HUGE jump above the GBA, while the graphics weren't comparable to what the PSP had there was still a pretty big wow factor when switching from GBA to DS simply because of the slightly larger screen better sound larger color pallete and most of all the simply fact that it could render 3D.
The Wii on the other hand, with the exception of a few games, hasn't really shown itself to be truly capable of delivering anything more then the GC. True it is double the power of the GC but it's questionable of this graphical leap is at all comparable to the DS were they added in a faster processor and enabled new things like 3D processing (Wii goes faster has larger memory but we're not hearing much in the way of new shader support or anything like that).
However I would also argue that the Wii has made some concesions to offer more then JUST the controler, after all Nintendo did increase the hardwares speed and memory capability along with packaging in some flash memory and wireless networking. They are setup to do firmware updates and online gaming will eventualy come. Here the weakness isn't that they arn't offering anything besides interface the problem is they're taking their sweet time getting around to delivering on any promise besides interface and developers are following their lead.
Nintendo talked about doing Wiimakes (GC ports with controls patched on) and putting gameplay above graphics, is it any wonder developers are following that advice? Nintendo might be able to pull it off effectivly but others might not be able to. If Nintendo at least offered online support I might be more tolerant of Wiimakes since they could at least delever new ways to play in several different ways but when it's just the control scheme it dissapoints (Prince of Persia I'm looking at YOUUUUU)