My guess was that it was to do with places selling pre-orders that they didn't always have the supply to meet (that is, StoreX sells 100 preorders of something, someone's 90th on the list, StoreX only gets 50 copies at launch, and doesn't finish meeting the 100 preorders until a month later or whatever). But your scenario with regards to PayPal length of coverage makes sense too.
Either way, yeah, it's obviously a newer rule (one of the more recent updates - along with the Alpha/Beta thing that's its own thread). Just figured I would mention it.