Xbox One does not include a headset in the box because every console includes Kinect, itself sporting an array of microphones up to the task of enabling voice chat, Microsoft has said.
"Xbox One does not include a pack-in headset accessory," Microsoft told Ars Technica. "Each Xbox One includes the new Kinect sensor, with a highly sensitive multi-array microphones designed to enable voice inputs and chat as a system-level capability, both in-game and with Skype and other experiences."
The statement concludes: "For gamers who prefer a headset, we have a variety of offerings that you can find on the Xbox Wire."
PS4 does what PS3 never managed, bundling a headset with every console.
The problem with relying on Kinect for in-game chat is that you'll be forced to have the voices of players coming through your regular speakers, rather than the earpiece of a headset. Microsoft could have solved this by making the Xbox One compatible with existing Xbox 360 headsets, but instead is hoping gamers cough up more readies on a new headset.
Source: Ars Technica