See Nintendo launching in 2011 would kill momentum for the Wii, as Nintendo can't support two consoles at once, and third parties would only develop for the newer system, and the small price difference and BW compatibility would result in people preferring the new system and it would give MS and Sony a chance to see what Nintendo was dong and release something to counter, thereby possibly preventing Nintendo from gaining the control the Wii has.
Better for Nintendo to launch last and disrupt the PS4 and 720, when they try to compete with the Wii.
The reason the GCN failed by launching a year later was it wasn't different than the other systems, it was too similar and didn't disrupt, Nintendo's next console has to have something different, something disruptive, so launching later would be a good move, makes it harder to copy.
Predictions:Sales of Wii Fit will surpass the combined sales of the Grand Theft Auto franchiseLifetime sales of Wii will surpass the combined sales of the entire Playstation family of consoles by 12/31/2015 Wii hardware sales will surpass the total hardware sales of the PS2 by 12/31/2010 Wii will have 50% marketshare or more by the end of 2008 (I was wrong!! It was a little over 48% only)Wii will surpass 45 Million in lifetime sales by the end of 2008 (I was wrong!! Nintendo Financials showed it fell slightly short of 45 million shipped by end of 2008)Wii will surpass 80 Million in lifetime sales by the end of 2009 (I was wrong!! Wii didn't even get to 70 Million)
