Check Out Why The PS VITA Doesn't Have 3D

Speaking to GameSpot, Michael Hocking suggested glasses-free 3D gaming only works when keeping your head still which only takes away the Vita's use of SixAxis motion functionally.

"We wanted to offer a really, really high-resolution OLED screen, and the best way to do that was in 2D. At least for the first one," he said.
He also mentioned about the 3D support in general quoting:
"A message we’ve been giving to all of our PS3 developers is add 3D where it adds something to the game. It’s not a tickbox we want on all the game boxes; we want 3D to add to the experience. The other really important thing is to do it well,” he said.

We also think that another reason the PS VITA does not have 3D, is because of the 3DS, most likely Sony want to give consumers another reason to purchase the PS VITA other than 3D because they want consumers to buy the PS3 for 3D. 

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