The real reason why Nintendo's got the competitive advantage right now is money.
Nintendo is in an extremely healthy financial situation while Sony and Microsoft lost billions on their consoles. That means:
a) Nintendo can launch a new console whenever they want (from a financial standpoint that is) while Sony and Microsoft have to regain some of the losses they've made with their consoles. Both are big companies with lots of profits in other divisions but neither investors nor managers will like the idea of a product seeing a successor just when it started making some money. Going by a typical product life cycle PS4 and Xbox3 wouldn't make sense in the next one or two years. Also Move and Kinect just launched. Killing them prematurely would screw customers over.
b) Unlike this generation Sony (and probably Microsoft too) should hardly be able to sell their next generation consoles at huge losses. Try tell your investors "we've just lost billions with our product. Now let's do the same again with its successor!" It would be insanely stupid for them to do so. Consequently Nintendo's next console won't lack behind much from a technological standpoint.
c) Nintendo can greatly expand their R&D budget to create more franchises and release games at a faster pace. Considering Nintendo's ability to pump out 10 million sellers this is a huge advantage over Sony and Microsoft. The 3DS line-up already has 3 (or 4 if Brain Age is real) potential 10 million sellers listed and that's only for 2011. The competitive advantage of such a software line-up is clearly there.
