All products that are mass produced have lemons occur in the production runs - even Apple stuff (like my Macbook Pro where the logic board was faulty resulting in the fans never going on because the temperature sensor was not sending accurate temps to the CPU - result was a laptop where the logic board eventually burned up and I got my hand burned to boot).
Apple has been having issues with their damn logic boards for as long as I can remember. Went down this mess with them with two different laptops: orignal purchase and the replacement laptop. I did not have one as nice as you did/do, I had the iBook, but man talk about issues and of course apple's stance, "you must be using it wrong", Walnut Creek Store "genius" actually said that to me.