Null, most public companies have a thing called a "Board of Directors" made up of ALL major stockholders in a company. I believe Sony would have a member on that board considering they do own 1/5 of the company.
And if you really think Sony doesn't care about who Square develops for you are NAIVE. Square's RPG's have become one of the most recognizable titles worldwide for Sony's consoles. If you think they wouldn't step in and try to flex their "in the restraint of trade" muscle to stop them... well... thats worse than being naive. I'll leave it at that.
Sony has risked far more to try and squash the competition, like threatening retailers with not providing them with PS2's. Hell, look at what they did to the Sega Dreamcast. If you think the PS2 won just because it had a better brand name, you're kidding yourself once again. Using influence they have in a company to influence a major player worldwide in gaming, well that would be far too easy.
As for Square developing for only 1 console: Things change. If you haven't noticed "exclusives" are quickly becoming a thing of the past. We are coming into a gaming age that not only appears to have 3 consoles which are going to survive, but THRIVE. I think the way developers like Square treat consoles is going to change substantially very soon.
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