FIRST TIME POSTER HERE! :D
Anyway, I'm just going to say, the whole thing makes sense.
Was it not slated to be released in 2015? the same year Uncharted 4 is poised to be released?
Tomb Raider, as good as the reboot was, will probably never sell as well as Uncharted. I believe that franchises have lifespans and I think Tomb Raider hit its end years ago, which is why with the reboot they attempted to take Uncharted's direction with the game.
If it's a timed exclusive, and it may just be, I'm sure it would arrive on PS4 and PC within a year from the Xbox release.
If not, then hey, sucks for Tomb Raider fans, and for the developers. I think that there are specific genre enthusiasts that are associated with each console. Sony typically has the action/adventure, story driven games, while Xbox tends to dominate in the FPS area. I do think Crystal Dynamics is over looking this.