First of all, IMO engine timing belts that require periodic replacement are an abomination in the realm of internal combustion engine technology. The mechanical element that ensures coordination between the rotating/reciprocating assembly and the valvetrain should be designed with an indefinite life expectancy, or at least one commensurate with the engine's bottom end. However, the bean counters, allied with the NVH experts, already have prevailed in many cases.

To design an engine with a known and likely (timing belt) failure mode that will cause secondary, catastrophic failure (piston/valve interference) is, IMO negligent on the part of engineers, albiet in obedience to management.

Now if you have one of these failure targeted vehicles, and knowingly elect to await the failure instead of performing the scheduled maintenance, I'm at a loss to understand the rationale.
The direct cost as well as inconvenience of allowing this to happen at a time of Murphy's choosing could be staggering. Family road trip hundreds of mile from home? Driving to job interview or new job? Evacuating from a disaster?

Since I do my own auto maintenance, on the one vehicle that happens to feature one of these abominations, I replace the timing belt on or ahead of schedule, and especially any time that I'm doing any other work that exposes the timing belt for easy replacement. It is only a $10 part, and is about a 30 minute job from the word go. That's part of the shame of it, it is cheap and easy to replace (as well as expected to fail) like spark plugs, but is a much more mission critical item in that, unlike spark plugs, it gives no warning before leaving you stranded on the side of the road with a expensive tow and/or repair.

Sorry for the thread hijack, I guess I was provoked!