Nintendo does this to drive up demand - Sonys problem is even 1mil peripherals is only going to drive 200-400k sales of a big title - not big enough for the investment of any third party to do a real AAA game, which could get big momentum for the platform. So you have to invest a lot in first party games to sell the platform on a relatively tight budget. Thankfully they have the money to throw around now, unlike the PS3 days.
This might make sense if we were talking about actual exclusives, and if we're talking about VR-only games, you're absolutely right.
But AAA studios can approach VR as something of a hybrid experience. It requires some development, but can be retroactively applied to a lot of existing games and engines without a huge amount of additional effort. They can budget VR more like a port, and less like an entirely new game from scratch. The PC community is helping out a lot with this by retroactively patching older games with VR support, and in the process very rapidly iterating on control schemes and camera parameters to make it "work" in games that weren't originally planned for the platform. Games which support VR can also support traditional controls and regular televisions, which expands the market for those who just want to play the game, and don't want to pay for the immersive headset.
It's an interesting space to be sure. I definitely think Sony was wise not to over-produce headsets initially for such a new, untested platform, but at this point it's pretty clear that VR is going to continue to be a thing. I don't know if it will ever hit actual mainstream / casual gamers, but there's enough passion in the product from the hardcore customer base to keep the momentum going.
Yes, you can do that, just like adding support for say the PlayStation Move or 3D TVs. That doesn't equal a good experience though necessarily. So many game experiences suffer in VR if you're not designed for it at the start, and jutter/motion sickness is a real concern in VR.
VR generally wants you to have a slower paced first person view, if the player isn't in a cockpit of some sort and in a "natural sitting" position. Racing and flying games have this and are naturally good VR experiences if the engine will allow for it (not all do). But all 3rd person games are out. Most FPSes are out. Thats a good chunk of the industry.
VR definitely needs to be developed for intentionally. Not least because the performance requirements are significantly higher.
However VR isn't really restricted to a first person view, you definitely need to respect motion sickness and avoid it as much as possible but there are plenty of good games that use a third person viewpoint on the action. What you really shouldn't do is take control of the camera and when you do (e.g. for locomotion) avoid styles that cause nausea.
FPS games actually work great if you get the motion control scheme down. Initially FPS games didn't work well until people came up with good solutions to this.
