They compensate for this with reprojection. If the off board hardware hasn't received a new frame within 8 milliseconds of a move event, they reproject the existing frame moved over by the delta of the move event. I assume the thinking is that you're mostly focusing on one spot, so this ends up "moving" correctly even if the image as a whole isn't quite right (edges cut off or whatever).
This is mostly correct. The games actually get a choice about how they want to render
Most games will choose to render at 60fps, the game reports this to the OS and then the headset will know to reproject between each frame, so the game gets plenty of time to get the next actual frame ready.
Some games will do 120fps though, not sure who will pull that off voluntarily though!!!
