My timing chain broke at 149,000 miles. Is this normal?

We didn't hear any noise, the car bucked a little then the engine just stopped. Unfortunately we were driving on a highway doing about 70 mph. It did not over heat or lose oil pressure. The cam is damaged as well as the head and timing gear. We don't know if the valves are damaged or not but the mechanic thought they probably were. Everything I have read says the chain should last the life of the car. Guess not in my case since the chain killed my car.