I own both and you're right. There's really no reason to do so for most people. In my case there's Xbox One games like Quantum Break that I want to play that I would be unable to on the PS4.I just don't see a reason to own both a xbone and PS4 unless you get one for dirt cheap. Most of the games will be the same. It's not like Genesis/Super Nintendo or Playstation/Saturn/64
As of late I've been using my Xbox One more than my PS4 but now Second Son is out so that will change.