I don't mean to be a negative nancy. I love Xbox. But damn, they've lost a lot of third-party support.
The vast majority of Japanese games will skip Xbox.
Xbox gets a lot of indie games and Western third-party devs, but there are still an alarming amount of them that skip Xbox.
The Talos Principle will never be on Xbox (indie dev). Transistor and Pyre will never be on Xbox (indie dev). Dust An Elysian Tail (former 360 indie game) got a PS4 port - no Xbox port in site. Same with Fez. The new Hellblade game is also skipping Xbox completely. There are tons of these small little indie games, Western third-party, and Japanese games that skip Xbox. It adds up.
I think with indie games though, Xbox gets excellent titles. But I think overall the major problem with Xbox is the following:
1) If there is any indie or third-party game that comes out first on Xbox, there is a 99.9999% change that it will come out on PS4 eventually. Devs would be stupid to miss out on the "biggest" fanbase right?
2) If there is any indie or third-party game that comes out first on PS4, you can safely assume that 75% of the time it will skip Xbox. Sure you'll get excellent titles like The Witness, Thumper, What Remains Of Edith Finch, Firewatch, etc... with late ports. But ugh, those ports tend to remain secret for so god damn long. And they are few and far between.