Going into the final two months of the year, the oldest product for sale in Apple’s mobile lineup will be the 15-inch MacBook Pro with Retina display, which has been on the market for a mere four months. Apple(s AAPL) is also selling an iPhone 5 and iPod Touch and nano that are just one month old, and November and December will bring a brand new iPad, iPad mini, iMac and Retina 13-inch MacBook Pro. It’s probably the biggest single product turnover Apple has ever done in such a short amount of time. But such a remarkable transition also has costs: Apple will, for what the company believes is a short while, make less profit on these new devices than it did on their older siblings.

Following the release of Apple’s fiscal fourth quarter earnings on Thursday, the company also forecast the results for the next quarter. While it predicted it would…