I can't imagine Apple would cover any of its products longer than 3 years. In my experience with macs, they last a long time. If something is gonna go wrong, it will probably happen within the first month (like all those random Macbook problems at launch), and you will be covered.
With Best Buy, they know that most of their products will crap out after 3-5 years. So their warranties for specific items tend to last just before the breaking point.
Apple and other retailers usually only cover iPods for two years, because the lithium ion batteries only work for a couple of hundred charge cycles, and they want you to pay for a replacement battery, or a new ipod.
I don't wanna sound cynical, but that's how warranties work 😱