I am finding that the cardboard cases ARE more durable. I have had too many broken cases in the mail, and even after I got them in perfect condition. Thing happen to them. The jewel case is an engineering disaster.
I guess I must be lucky. I’ve thousands of CDs – the majority have come through the post (including lots from Europe) and I’ve had very, very few problems with damaged jewel cases. Way less than 0.5% I’d have thought. Not had many ‘in use’ failures either. A very long time ago I bought a whole pile of spare jewel cases of various capacities from 1 to 4 discs should I need to replace any that broke. That was a waste of money – I’ve barely used any of them! I still buy several new CDs a month but have never seen a cardboard case.