Publishers. Making a game like Bioshock or Assissins Creed would not make enough money if it was released only one one machine without funding by the hardware manufuture.

Well, I don't care if is MS or another company, but it's better to have more than one competing. Monopolies are good only for the one that has it, never to the costumers. Even thirdy parties want more companies.

to me another "big" must enter in the race.

If MS (or Sony) left, then Ninty would become more aggressive again in regards to console power and making sure 3rd parties are happy / 3rd party games NOT GIMPED on their platform. But as long as the big 2 are involved, Ninty will be out of that race (sadly)

Less competition is never a good thing.

the industry will always copy good idea.  sue me.

So why is it a good idea to have one platform then?

I honestly cannot think of one negative outcome of competition in the business setting when it comes to consumer welfare. I mean, there might be a few instances where it isn't a good thing, but I simply can't think of any of them.

Clearly the missle thing was a joke, but you missed the point.

Sony made the most powerful system it could at the time, so powerful infact these silly stories came out.   Sure more powerful system came out AFTER the PS2, but that's a given.  Sony created a very power system (just look into PS2 coded shaders for an example) even though they doinated the industry and had no idea what anyone else was plotting.

well, as a gamer i like to have options. I like to see what different companys have to offer cause they are unique. I want all three to do well.

saying Nintendo is irrelevant is mind blowing. You underestimate the power of nintendo first party software.