Have you been following things like sales and paying attention to what's under development for the Wii?
It's basically where the DS was a year ago. Development is declining, interest is declining, and sales are typically down each month.
They just reached such a high peak that the downward turn for the Wii is going to be a long one with many months of healthy system sales. But I think all the signs indicate Nintendo and consumers are just about ready for a replacement (Personally, I'm betting on an announcement in the spring of 2012 with a Fall release in mind).
Take a look at Nintendo developed projects we have to look forward to in 2011. Granted there should be a few surprises we're not aware of (Such as hopefully some sort of release to celebrate the 25th anniversary of the Zelda franchise that they've hinted about), but their slate was never so thin at this point in the year in years past.
The Legend of Zelda: Skyward Sword
Kirby's Dreamland
Fatal Frame 2 Remake (Sadly, it's all but certain we won't get that one)
Rhythm Heaven (Seems likely to be another Japanese exclusive after the DS title underperformed)
Pandora no Tou: Kimi no Moto e Kaerumade (No clue, but my money is on it staying in Japan)
Mario Sports Mix (Nintendo published, not even developed in-house)
The Last Story (Nintendo published, expected to be Japanese exclusive)
Sorry, but I think just looking at their slate of releases says it all. We're in the Wii's last year of being Nintendo's flagship console. They're clearly in the midst of WiiHD development unless they have an awful lot of projects to unveil in the coming weeks (Such as at E3) that are due later this year and the early portions of 2012.
You could see the same thing happening to DS development by them well before the 3DS was even officially announced.