So I guess I'm not the only one.
Bought my 4th gen in Edmonton in July last year (4hr drive from home), had only owned it for an hour and hadn't even left the city yet and got my first rock. By the time I was back home it had already spread by 6inches. By winter had another crack from the other side and the first one had gone all the way across.
I've had my 3rd gen going on 6 years now, still no cracks. Have had multiple impacts, some loud enough to almost leave your ears ringing after and all that's left is some stars. I have 5 or 6 stars but still no cracking.
Leaves me to beleive that they must've cheaped out on the glass. Luckily up here there's not much for safety type enforcement so I'll just tough it out till I get a few more then I'll switch it out.