Re: "a design defect that causes the battery life to diminish"
Um, not defending Apple by any stretch, but I do believe that battery life tends to diminish with or without design defects.
Your average apple customer doesn't know that - I imagine $200 vs $50 and the advertising claims durability and long life (along with the usual unspoken apple lifestyle promises) - you expect the battery life to be three times longer.
It's the Samuel Vimes 'boot's issue - and someones noticed the expensive boots are cardboard, not hard wearing leather.
Apples over-hyped claims have come back to bite them.