If I'm a prospective console buyer who cares about indie games, why would I go for the Xbox One? With the PS4 I know that I'll get to play the indies that release first on PS4 and sometime down the road I'll be likely to play the indies that released first on the Xbox One. If I were to buy an Xbox One, I'd get the indies that release on it and then nothing else. Every trailer I saw for an indie releasing on PS4 would just make me regret my purchase because the parity clause prevents me from ever playing it.
Case by case basis. If it's a truly worth it game to play, most of the time it'll also come to Xbox One.
Of course, there are exceptions to both sides (Velocity 2x, Max:CoB, etc).