Prior to the original Playstation, Sony was actually working for Nintendo developing a prototype that could bring CD media to the SNES. Long story short they had a disagreement, Nintendo basically said forget it, so Sony just went off and revised their creation to be what became the original Playstation, see this link.
So if Nintendo would have been a little more lax, and gave Sony the deal they wanted, they would have actually been partners.
Then Microsoft actually approached Nintendo about partnering up(just before they made Xbox) and Nintendo said no, so as a result Microsoft made the original Xbox on thier own. See this link.
Had Nintendo appreciated Sony more, and was willing to work with Microsoft, there would be no Playstation or Xbox, but instead they would have both Sony and Microsoft working under their umbrella of what would be industry dominance. But instead they are competing with both brands which have proved to be quite the powerful foes in this sometimes harsh industry.
