Considering how similar the PS4 and XB1 are, it makes no sense to not make a XB1 port.
Yet there's a ton of developers not making XB1 versions of their games. Looking at the upcoming games I saw the following:
Ultra Street Fighter 4
Legend of Kay
The Talos Princess
Samurai Warriors 4-II
And these are just the ones with confirmed release dates over the next couple months, The list gets worse when you also count stuff like Dragon Quest Heroes, Persona 5, Hellblade, Yakuza, etc.
Sure we can keep pretending these don't matter cause they're not 10 million sellers, but the fact is people are buying the PS4 cause it has all these niche titles releasing every week and they appeal one section of gamers or another. MS needs to put more effort into enticing developers to release these games on XB1, Halo and gears will sell the console only to so many people most of whom probably already have it.