Messy maybe.  But it seems like they have a system that isn't too hard to understand.  Pre-order does matter, it is used to determine your placement in the queue.

Examples:

Pre-Order #1 pays for his Jupiter today.  He is in the 7 day window, he will always be #1 in the shipping queue.  Even if Pre-Order #2 paid before him.

Pre-Order #501 pays for his Jupiter today.  He is in the 7 day window, he will be no worse than #501 to be shipped, unless someone with a lower Pre-Order number fails to pay.

Seems relatively easy to understand once I got that confirmation directly from KnC