what ur saying doesnt really make sense, why does Nintendo NEED to give Wii U a 6 year life? SNES/N64/GC all had 5 years. GBA only had 3.5 years and the successor went on to be the best selling handheld of all time. Xbox had 4 years and its successor went on to sell nearly 4x as much and gained a ton of marketshare.
Nintendo can easily get away with releasing a successor after only 4-5 years as long as Nintendo themselves releases a solid amount of there own ip.
They need to release at or near the same time as the rest... You release to early and run the risk of showing your cards to soon. Also, comparing handhelds to consoles is kind of moot...
The examples you are giving are very vague and had many other factors that came into play...
The 360 was rushed and could have used the extra year... MS got a year jump on Sony and Nintendo but it could have backfired and that year advantage helped but Sony caught up and Nintendo crushed them both.
How has the year jump helped Nintendo this time? It has not! They should have waited. Launched with a MUCH better line up. Nintendo is better off taking the extra time and putting it into the console and shoring up the launch offerings of the next console. Releasing a year ahead of everyone else is only going to blow up in there faces... and again Nintendo made truck loads of money on the Wii, they can afford to be patient. Besides just because the WiiU is not profitable now does not mean it will stay that way! They will start making money soon enough and the new 3DS will turn on the Nintendo money tap again.
The only people that want to new console so soon are graphic whores, Nintendo is not about that... never really have been! Nintendo does not need to pander to that bull shit.