At this point, a very strong argument could be made that Nintendo does not need third parties for success - in fact, the opposite may slowly be becoming true.

Hardly.  They've set up a strong system (and handheld) and made a whole new wave of first party titles.  But they need the third parties to secure success for the long term.  Or else, they will be in the same state Sony is in this gen and they were in last gen.

There will never be a time when its just one company making the console and all the games.

Feel free to elaborate as to why.

That wouldn't bother me.

I edited my post.  And I also said why in my first post.  Even if MS and Sony drop out, some other company will try their hand at making a console to compete with Nintendo.  And Nintendo never wants to be the only one making games.

Obviously, but the implication of "But they need the third parties to secure success for the long term.  Or else, they will be in the same state Sony is in this gen and they were in last gen." is that Nintendo is dependent on third parties for survival, when this generation so far has clearly shown that third parties, at this point in time, are not able to decide the course of a system's life. If they could, the Wii would already be dead.

Its not that they need Third parties to stay alive, I said they need them to secure success for the long term.

Nintendo has already gone through two generations with little to no third party support (the N64 and GameCube).  This shows that they can 'survive' with little to no third party support.  Now what they need to be successful and go beyond simply supporting themselves (and frankly the industry) is that third party support.

Would this make Nintendo's console the most hardcore?

I don't think this will happen anytime soon. If Microsoft and Sony left, another one or two would take their place. This is how it's always been. The gaming industry is successful enough for a different huge corporation to give it a try now and then.

Three. Three generations with little third party support. N64, Gamecube, and Wii. 

The fact that the Wii is successful, and not just "surviving", shows that the 3rd party level is not an important factor, there are other reasons behind Nintendo's failure and success.

You are simply stating something that you believe to be common sense, without any evidence supporting it, and when there is evidence against it, you simply add "it will only happen in the long term".

This is not different from the old doomsaying of 2006, that "Wii graphics will get outdated on the long term" "HD price cuts will kill Nintendo on the long term"  "casual gamers will get bored on the long term", or "the HD consoles will have even more killer games on the long term". 

You expect different results from doing the same thing over an over again. :P

It is just not going to happen. :)