If the shop guy who mounted these had used the same wrong jig setting for both skis, it's possible that both skis would have had structural weakness at exactly the same points. You could tell this from inspecting the ski.
The other thing is that from the pic - it might just be the angle of the pic, but it looks like those bindings are mounted too far back on the ski. That could cause this kind of crack, as the ski is stiffened differently at different points, and if the plate that is supposed to be under the front binding is instead in front of the front binding, you could get this kind of crack easily.
Taking the ski to another shop where they know what to look for will answer these questions really quickly.
I don't think it's the manufactuer's defect that would be identical on both skis like that, although, once shop error from the mounting is ruled out, I'd say a large part of it is that the ski just wasn't spec'd to handle whatever you hit - whether it was a "real" ice-hard mogul, or an ice boulder on the edge of the cat track. In my opinion, if you design a ski with a limitation like that, it's not a good candidate for a rental program, where people are usually beating up the equipment. If you sued them over it, a critical piece of evidence would be how many times they have had this particular ski returned with a break like this. Why do manufactures design a ski like that? To reduce cost for private beginners who are going to be careful with their equipment.
Whether it was you or the person who rented these particular skis before you, these skis hit something they weren't designed for. If that something was part of the expected terrain you were going to be skiing on - i.e., simple groomer with some ice chunks, not a double black with 30+ inch moguls, then I think the risk of loss should be on the guys who chose this ski. If it was your own private ski, the loss should be on you, not Atomic, for choosing the wrong ski. If it was the rental shop who might have tried to update their stock on the cheap, it should be on them.
As far as the damage waiver from the shop, that bothers me the most about this. I've only seen this kind of break once where both skis had an identical break. They were rentals, and it happened at Ragged Mountain in NH for spring skiing. Their slopes were literally lined with 20 inch granite boulders. My friend, who had never skiied before, skied off the edge of the trail, as beginners are wont to do frequently. He wasn't skiing fast, just "forgot" how to turn - skied straight into the boulder and cracked both skis just like yours. Never even released from the bindings. He had checked the extra damage waiver, and when we took them back to the shop not only did they not give him a hard time about skiing into the boulder, but they handed him another pair of rentals and said something like be more careful or you'll hurt yourself. No way any ski is designed to hit a boulder like that, but they understood the situation wasn't his fault.
So the fact that a shop would treat you like this after you paid for the insurance makes me not trust them.
It being the age of yelp and facebook, etc., I would make sure in your letter to the shop manager (make it polite and professional) that you plan to tell everyone you know about your experience and to avoid their shop. That means a lot more today than it did 20 years ago.