To be honest in hindsight I think both the DS and Wii were left on the market without successors for too long.
DS should've been replaced in 2010 and Wii in 2011 and they should've been better prepared (software planning) for both transitions. Their brand momentum was hurt by waiting so long, Wii in particular.
In this day and age you can't leave a product out like that for so long, and in Nintendo's case I think it was doubly damaging because they were relying much more on casual players ... suddenly smartphones/tablets show up and they seem much more exciting ... they are refreshed more frequently and have far more game/app releases all the time, it just feels like a much more dynamic, exciting ecosystem to the casual layman who doesn't care about playing "deep" games.
