Maybe because they finally realized they're not the king of electronics anymore. There are 400 million iOS devices in the wild, and probably as many or more Android devices - there are only ~75 million PS3s. SONY
needs to play ball with the customer in order to succeed.
Still, they'll have their share of proprietary hardware. By the looks of it, the I/O headset port on their new controller is proprietary.
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While I am glad they went with x86 platform, the question of pricing remains. Some speculate that the PS4 will be as much as $999 for the top-ens SKU which would be just ridiculous in our day and age.