Why would Nintendo announce and probably release the 3DS this year when the DS is still doing incredibly well (better than the Wii right now)? I don't think everyone in here have Nintendo figured out as well as they think.
I don't either, of course, but its worth to reflect upon. If anything, the recent 3DS coverage shows that Nintendo are not above launching a new console while the current one(s) is still in a favorable position, the DS is the most successful console in history after all. The DS is on safer ground than the Wii in a few ways with its higher installed base, the massive market share and incredible 3rd party support and still blazing sales but is due for replacing (seemingly, at least according to Nintendo themselves) and the implementation of 3D shows that Nintendo is not above following trends and development either, further strengthening my belief that they will not be slow to release their next console if only for the simple reason they don't want to be left behind (we saw how much Sony's delays cost them in the end teamed with the price of course). The PS2 was doing superbly, better than any other home console in history but that didn't stop Sony from developing and planning to launch their next console at the same time as the others. People in here love looking at the past and impose it on the current generation for beneficial purposes (in fact, the PS2 is often used to demonstrate the Wii's success) but the past also shows that the market leader is not above launching at the same time as others. The notion that Nintendo will launch first is arguably silly, there's not much supporting such a claim but as mentioned above; the 3DS comes at a time where the DS is still reigning supreme (a lot more so than the Wii ever has and ever will) and there's still no good word on a PSP2 (yes, the PSP launched later, we all know that but that's not the point) as of yet. There is also the point that developers would not want to be stuck making games for a console that is effectively two generations behind the current hardware standards, which will surely force Nintendo's hand somewhat given their less than optimal relations with 3rd parties on their home consoles.
Yes, there are those who think that Wii sales will suddenly drop drastically but there are even more people who seem to resent the notion that Nintendo won't do exactly what they want them to and think they'll do; keep the Wii alive a lot longer than its competitors.
Personally, I don't think Nintendo will launch their next console before the others but I don't think they'll launch it later either and I remain sure that this generation will be much shorter than people expect (a lot of folks see this gen lasting ten years, I do not, 6-7 at the most).