The iPhone company explains that for its products environmental reports, it assumes products from its iPhone and Watch lineups will be used for an average of three years. Its computers, laptops and TV devices on the other hand have a projected lifetime of four years. Perhaps these statements offer some clues about the projected lifecycle requirements Apple uses when designing new products.
To model customer use, we measure the power consumed by a product while it is running in a simulated scenario. Daily usage patterns are specific to each product and are a mixture of actual and modeled customer use data. Years of use, which are based on first owners, are assumed to be four years for OS X and tvOS devices and three years for iOS and watchOS devices. More information on our product energy use is provided in our Product Environmental Reports.