That's exactly right. If you're going to make a product, it had better be safe under expected conditions. A keyring with many keys might not be common, but it is not wildly abnormal.
Sort of like designing a set of stairs. It's not likely that three 400 lb people will be climbing those stairs at the same time. But you had better design for that possibility.
“On a Clear Day One Can Foresee Forever.” a law school article
And when three 600 lb people cause it to colapse after 900,000 people use It with no prob, who should be blamed?