Playstation cases and CD cases (and probably dreamcast cases) are made from unexpanded polystyrene, which is a rigid if brittle plastic. All will probably scratch, detach and possible shatter if dropped onto a hard surface at just the right angle. The problem with EU dreamcast cases is two-fold - their increased weight thanks to their manuals containing so many languages (and coming from the days when games still had proper paper manuals) which often causes the thin bridge between the front clear window (which is thinner than a CD case lid) and the hinge pin to shatter, and the disc holding spines are halved compared to a normal CD because the support holding two discs, one front and one back. Drop the disc in its case, even in quite bulky packaging, and the game disc will simply shear through the top pins. In my experience, a CD treated similarly will probably just detach from the spines, perhaps because they have a slight angle to them.
DVD cases are made from polypropylene which is more pliable than polystyrene and thus tends to bend under load rather than shatter. Thus they feature a different mechanism to hold the disc in place usually which only consists of two halves which due to being in a concave shape are also relatively rigid that require the user to press both parts with their thumb to allow the disc to be removed. This stops the disc from delatching when the case is dropped, which would probably be worse for a disc in such a case since it has much more space to rattle around in and the undocked spindle can scratch the data area, while a free disc in a CD case will probably just scuff up the central area.
That's true for EU dreamcast games - I've never had a disc become unreadable due to it becoming free floating inside the case. But there's scope for it especially with those little shards of spindle plastic floating around once the disc has bludgeoned its way off the spindle.
