I had a chain snap on an 84 Deville (w/ HT4100) @ 136k miles. Not the best example to use, but a chain CAN break. I had the car hauled off, I didn't even bother having it repaired. Timing belts are very reliable and the recommended replacement intervals set by the manufacturer are very conservative. So I had to spend a few hundred bucks every 90,000 miles to change the timing belt? Big deal... I spent way more than that replacing alternators, starters, fuel pumps, chasing/repairing electrical gremlins on my older GM vehicles before 100k miles. The only 'problem' really is the interference engine. If the belt snaps while your at 3,000 rpms tooling down the highway, you're likely SOL w/ a trashed engine. But, going back to what I said above, modern timing belts are extremely reliable and I have never had one snap on me... unlike the chain!