I've been studying timing chains for a while now, trying to gauge when I should start thinking about replacing whose in my household vehicles. When I saw GM 3.6L engine front cover off for the first time the impression I had gotten that they had made the chain unnecessarily long. Because of that, net stretching effect is greater. No wonder these GM engines are predisposed to an earlier chain failure. Contrast that with GM small block engines, where timing chain is very short. Those small block engines can run to 500,000 miles and more without an engine overhaul.
From what I've gathered thus far, provided that a vehicle is properly maintained, it's a spirited driving that contributes negatively to timing chain stretching over time. That's because during acceleration stress is highest, not surprisingly so.
Looking at this subject broadly however, I cannot not to think there is some automaker conspiracy going on here. I mean what in the world was wrong with timing belts? Taking a cover off and replacing a belt was a snap, and if you did it every 50,000 miles the engine could run forever. Well, at least the valve train wasn't the weakest link. So, automakers thought how can we make it so that engine is done once it reaches 150,000 miles or so, and no average Joe can fix it in his garage. And they said let's use a timing chain instead of a belt! Joe ain't gonna take front engine cover off in his garage just because he wants to replace timing chain early. The only time he'll want to do that is if there is a problem already. Even then, he'll probably go to a dealer and while he is there we'll just sell him a new vehicle.
But that didn't stop everyone and some people here and there started working on the timing chains on their own. Meanwhile, manufacturers started placing timing chains in the rear of the engine (latest audi v6). There you have it! Want to change timing chain? Try pulling the entire engine out first!
Bottom line, the unfortunate reality is such that timing chains do stretch and replacing a chain isn't an easy job. Proper maintenance and gentle driving will prolong the life, but will not stop the issue.