I was surprised; Apple wants to save paper, so they encourage online submissions and no UPC; if they made you send the UPC that would mean envelopes which defeats the whole point.
I bought my computer in February; they gave me a swap on June 1st because my first one warped, I went on June 3rd to ask if I could get the iPod still and they basically bought back the machine and resold it to me so it was on the same receipt.