PC has more hardware to take advantage of, and I guess Beth thought it would be beneficial to take advantage of Kinect on Xbox.
Its not "Free Content", they are just taking advantage of some things they feel help the game. Its more like updates.
Also, this post is kind of childish. Its like kindergarten when one child sees another with something, and then they start to think they are entitled to get something too. That's not always the case
Besides, if I were a PS3 player, I'd want Beth to focus on the framerate issue (if they haven't fixed it 100% already) rather than gimmicks like kinect/psmove support.