The first and largest is that the Kinect is a product differentiater. It makes the XBone different from the PS4. There really isn't that much a difference between the two boxes otherwise. Fine, you can go on with the technical differences between the types of RAM and the custom silicon for the XBone's APU but those are not large concerns for Mom and Dad buying little Sally's birthday present.
Until MS comes up with something besides the software that makes their product different, the Kinect is going to hang on. But the second that happens, it'll be tossed. They know they've screwed the pooch here. They know exactly what it cost them in terms of customer relations and in terms of developers.
My friend has an Xbone. It turns out Kinect is what caused his WIFE to monopolize it. Yes, his wife took over the Xbone. Playing Just Dance 2014, Kinect Fitness and other Kinect games.
Enough so it's hard to get him on his Xbone. (And apparently, his youngest kids are all seeing mom dance and doing it themselves. And no, he's responsible - they take their kids outside to play which is why his Xbone gaming time is limited - they purposely want to keep their kids from getting addicted so they only play normal games when the kids are in bed).
Apparently they also really, really, really like Skype on it - the Kinect "zooms" in on the person speaking.
Of course, a popular peripheral for the PS4 is the camera - which if it isn't used to stream amateur porn shows on twitch...).
I have both, and find myself playing the Xbone a lot more than my PS4 - the camera's just so-so ($60 for what amounts to two $10 720p webcams...), and PS4 controller battery life is atrocious.
The only really bad thing is, on the PS4, I'm not buying games on it - I'm just waiting for them to show up on PS+. I did buy two games, though, but those were on ridiculous sale.
And no, the "p"s don't matter to me - because I end up playing PS4 using my Vita and remote play - about the best feature the PS4 has over the Xbone. But it also means the p's don't matter because ou're just squishing it down to quarter-FHD (540p) for display on the Vita screen.