Low persistance displays are a tricky issue.
They obviously don't have the issues that high-persistance displays have of holding frames for too long. However, they have another annoying effect, commonly referred to as the strobe effect. This has to do with each pixel being lit for only a minute duty cycle on the display. This causes bad flicker at low refresh rates.
Early low persistance displays obviously were not very good on this issue. This is because the displays used very slow technologies such as oscolating mirrors.
By the details I've read on their blog, I'm pretty certain Valve has gotten down that they need a high refresh rate to get the VR to work right. They have identified strobe effect as a problem, and have identified that while the traditional 60Hz rate, while tolerable, is far from ideal for low persistance displays. They seem to believe they can push the refresh rate high enough to deal with strobe effect. I have confidence that they can.
Higher refresh rates also have other advantages for gaming as Internet router designs improve and ping times drop, the latency produced by interpolation becomes more substancial, and the best way to reduce it is to push more physical frames. If you are pushing more physical frames, there are clear advantages to pushing more visual frames to match.