A lot of grumbles and groans have been directed at Microsoft for forcing users to buy the Kinect 2.0 sensor when buying an Xbox One. One reason for this is privacy- amongst talk about the NSA snooping data and Microsoft having an online connection, there's a reason to be concerned- but the other reason is much more consumer-based, and this comes down to price.
This is one of the reasons Shuhei Yoshida of Sony decided not to include their camera with the PS4, saying that "Rather than forcing every user to buy the camera, I think it's better to to allow a separate purchase just for those that will enjoy it. Selling the camera separately means that the main console can be more affordable."
Yoshida also believes that making the camera mandatory is a bad choice right now as it is a medium that many have yet to adapt to- "I believe, and this is personal opinion, that for a technology to gain universal acceptance a certain degree of maturity is required. For instance touch control has been introduced a long time ago in machines like ATMs, but it wasn't as easy to use as in today's smartphones and tablets. I think natural interfaces will spread in the future, but I believe we to need identify proper uses for them first."
Personally I don't see the need for gesture controls and when using the Kinect, I found the experience both awkward and less convenient than the controller I was already comfortable with using.