Unfortunately it seems far more likely that Nissan made a calculated gamble when they opted to use an air-cooled battery pack for the Leaf and now it's coming back to bite some customers in the backside. +Chevrolet, +Ford Motor Company, +Tesla Motors, and +Fisker Automotive all going liquid cooled for their lithium ion batteries.

Heat is the enemy of lithium batteries. The loss of capacity is the result of overheating the cells which can lead to microfractures in the electrodes. That's why most other automakers are using liquid cooling to carefully manage the internal temperatures of the battery. Hopefully Nissan's problems don't do to plug-in vehicles what Oldsmobile did to diesels in the 1980s.