As an engineer I wouldn't be too concerned about a sudden failure on a bike unless it was due to a crash. These frames are engineered to well above whatever the rating is. Like said above lawyers overrule engineers in this kind of stuff all of the time. At 250 lbs I've never broken a road frame but I have snapped an aluminum mountain bike frame during a crash. And even then I was able to line the frame up and get it home without much concern.