Ten would be plenty but I'm struggling to understand why you think it's only ten. What are the 100 VR games Kaz spoke of?
What Hirai talked about are most likely VR-compatible games, just like there were over 100 Kinect-compatible games that Microsoft would tout as "over 100 titles available for Kinect." But there weren't over 100 games that you could only play with Kinect, most of them just had the "Better with Kinect" label slapped on the box because they had a few Kinect features. You know, it's basic PR speech to make the numbers sound more impressive.
But from a developer's standpoint, there's no reason why anyone would limit themselves to a device combo that necessitates a ~$700 investment from consumers and will predictably have a tiny installed base compared to the other available options. I highly doubt that those 100+ games are VR-exclusive, the vast majority of them will be VR-compatible, so you can play them either on a vanilla PS4 or with a few VR enhancements/gimmicks.