Having a three-way competition is beneficial on some level, even if one underperforms considerably compared to the other two (see: Sega Saturn vs. PS1 and N64). Even back in the NES days, there was a three-way competition (NES vs. SMS vs. Atari 2600/5200). And as MS was happy to show when Sega dropped out, there's always somebody willing to step in and fill the void. So losing Sony or MS would probably not have much long-term impact, because somebody would step up and fill the void before long.
Nintendo, on the other hand, is synonymous with console gaming and has been since the Famicom was released; they're the only one that's stuck around for this long. Their dropping out of consoles would have a profound effect on the market in the same way that dropping the discus toss from the Olympics would impact fans of the Olympic Games. Even at their most unpopular, Nintendo was still the first name that came to mind for many gamers when referring to console game companies, for their sheer longevity.
Sky Render - Sanity is for the weak.
