“As far as I can tell, the mountain bikers are totally silent on the
subject of these horrific accidents, and what they imply about the
danger of mountain biking. Am I wrong?
Yes, Ed, you're totally wrong. Mountainbikers are completely aware of the risks and post videos and pictures of mishaps. We choose to go out and live our lives and accept those risks.
Here's a compilation of the many that have been posted on Pinkbike ...
http://www.pinkbike.com/video/309875/
Glad I could enlighten you.