Paying in full at the time of a pre-order is something that I expect many will not do again. It is certainly a cheap way for a seller to fund its ongoing cash requirements, but at the very least it is unnecessary until the time that the seller has to pay the manufacturer for the goods, which in this case was probably when they were actually delivered fob in China. The downside for the pre-order buyers of paying in full, apart from the admittedly small opportunity cost on the funds, is that the seller will go bankrupt in the interim and all the pre-order funds will go poof.
I usually think of PRE-ORDER payment (partial) be a form of committment. Never thought the full payment was necessary. But I do believe it would of simplify the process when the product arrive, so there won't be a need to re-confirm and collect payment. Lack of comms is def a killer for business.