The speed is a result of circling into the rotor created on the leeward sides of slopes like these, on windy days. (not diving)

The winds were 40+ when these records were set. I don't know about you, but if I had a plane performing 30 to 40 G circles right in front of me, at 262 mph, I would want a bit of protection in place. (They may have those "barriers" for another reason, but they're a good idea, regardless.)

I'm not by any means an expert on dynamic soaring. What leads to my interest is how these guys build hollow composite wing structures that can take 40 Gs. (amazing)