I think one of Nintendo's advantages may be one if its disadvantages. Nintendo has made it known (various Iwata asks) that their hardware is centered around a vital software idea that Miyamoto has for each generation, and it is usually manifested in a mario title.
In a nutshell, the kinds of games Miyamoto makes are the kinds of games that mesh the easiest with the Nintendo platform. The xbox and playstation are business oriented machines and so they are not designed for just one kind of designer. Nintendo will always have a harder time getting 3rd party support because their concepts are much more specialized, even if inventive as a result(which I'm in agreement that the wii and ds are).
Just a little theory, but it is true that Miyamoto's software ideas have a huge part in the hardware creation.
