I am a big guy and always have been, I've never snapped a bar or stem and really haven't seen examples of others doing so that didn't involve being directly related to an accident. A lot of other issues don't tend to happen as a result of speed. I've only ever snapped 2 chains both due to lousy shifting under load but no accident. I crushed a BB, completely shattered the cup climbing a hill at over 18mph but other then the crank going wonky and slamming the top bar going uphill let me control the stopping a lot better. Also crunched a BB last year, more power then speed and so no injury. A lot of mechanicals when they go I bet are at slower speeds but when putting in the exertion to get up to speed or accelerate and result in less injury. Regular maintenance should also eliminate a bunch of the issues, like rims usually don't shatter catastrophically without some warning like going out of true from a nipple pulling out or the sidewalls being concave from wear letting you know you've hit a dangerous point. I always thought carbon forks would be a major issue and resisted buying one for years thinking they were just a failure point but I've had to give that one up, they've proven pretty reliable.