I made no false assumptions, but you did. The Smart Case is Apple branded (designed by Apple), not 3rd party. Furthermore, my legal education and experience tells me Apple would very likely be held liable on the facts I presented. As for warranties, there is what is printed by the manufacturer, and there is the law. They are not always the same. Trust me on that one, or do some research on the MMWA, implied waranty, effect of disclaimers, etc. and so on.
If I purchased an iPhone at an Apple store, and, on the recommedation of the salesperson, the case, and assuming for argument, the average battery life for the phone battery is four years, and assuming I followed the instructions, and assuming Apple did not warn me that the case would shorten life of the phone (battery), and the phone battery became unusable after say, two years due to the case, then I am around 99 percent sure that I would prevail on a claim. Either that, or I wasted three years and a hundred grand on a JD. Of course, as a practical matter, unless it went CA, litigation wouldn't be feasible, although there could be a possible UDTPA case. I have almost always had great success in such situations through preparation and stating my case to decision makers, walking out fully compensated. YMW most certainly V.
Back on topic, I plan on cycling the phone battery at least once a month, ditto for the case, and following all other instructions and best practices for bat mgmt. Therefore, I'm not too concerned and in fact, quite happy with the APPLE Smart Case. I just wish they made one for the 7 Plus too. There is a new bat case for the plus coming out from Fuze though, and it also gives you the headphone jack back. Waiting on initial reviews for that one.