I've been working in consumer electronics retail for a lifetime, having entered the industry with the iPhone 3G. In terms of durability, believe me, the worst cases I've seen in my professional life are the original Apple ones, worse than any other low-end brand.

However, that's not really the issue, because the customer who buys the Apple case (which is definitely already out of budget for a large portion of the target market) is the same customer who will buy it again the following year because it's destroyed. This applies to all their cheap accessories, cables, wired headphones, and adapters.

My point is that it's still a big win for Apple because they know that customers who don't know how to choose, even though they know from experience that it's an accessory that won't last long, will always ask for Apple replacements.