I'm confused - every company out there does this, why is this special? I mean, my Xbox 360 was struck by lightning and Microsoft got it picked up in an hour and two days later I had it back with an improved disc drive (which was not broken before) and half the stuff inside replaced. I got a new brand of motherboard when an old one broke down too, etc. etc. It's standard practice because, as has been said, they don't keep stock.
By the way, if anyone wants needs a mp3 player, get the Sansa Clip + - better sound than the iPod Nano, supports FLAC files, has a longer battery life, is a lot cheaper and supports a micro SD card.