When I see interesting exclusives X on Vive, Y on Oculus and Z on Playstation VR, I won't buy all three platforms. I'll just say 'screw you all, I'll pass'.
Valve has developed and supports the OpenVR platform[1], which is designed to allow different hardware on the backend. Rift/Facebook seems to be primarily pushing a closed platform with exclusives. Playstation VR is obviously Playstation-only. Make your purchasing decisions accordingly.
Oculus has exclusives because they partner with developers, offering money and support. Vive has exclusives because there's stuff you can do with the Vive's native VR controllers that you simply can't with the Rift's Xbox One controller.
When Oculus releases its Touch controllers (hopefully before the end of the year?) you might see Vive titles ported over to Rift. Movement in the other direction depends on what terms and conditions are in the contracts studios agreed to sign.
The ability to walk around something makes it seem so much more real. With vive you can duck below and look under a table, lean around, view something from all angles. With oculus you're limited to seated experiences so it doesn't feel much different than sitting at a desk with a 3d monitor.
Also, moving your character with a controller or keyboard can be nauseating. This is why the best oculus games are going to be "cockpit simulators" or they're just going to have a"virtual screen". The vives ability to move yourself with your own legs keeps nausea in check.
The Vive's entire ecosystem is set up for moving around, using your hands, and really being 'VR' like we've all imagined. The oculus is your head as a camera in comparison.
