I think the thing that most people forget is how global Sony is as a platform holder.
In a lot of the non US/Mexico/UK world, The Xbox Brand is basically about as alive as the Wii-U was last generation. MS generally doesn't do much to change this, and it's just been how it goes. Even during the 360 years, arguably the highest point of the Xbox brand, it struggled against the PS3, a system that basically shotgunned itself in the feet, because they just don't have the global presence to do the same thing Sony does.
Nintendo also is fairly global, but not on the same scale.
I think we'll see both Sony and Nintendo do very well next generation, too.