The purpose of that headset is to plug straight into the Xbox controller while still having a higher than normal level of audio "quality" (if you can call it that with a headset like this).
I would consider that a tethered wireless headset, not wired.
If I had to guess, the headset needs the battery power to drive itself better than the controller alone could, but still has to get the audio info from somewhere. No benefit in doing this over, say, a fully wireless model.
Theres a reason you dont see many with that sort of design. Either go wireless or dont.