Pre-orders exist in many cases to guarantee enough sales for a manufacturer to go into production. Without a minimum number of presales, some products might never be made.
The retailer in this case has commited to purchase the product from the manufacturer. Once the manufacturer has commited to producing the model, the retailer may not be able to cancel their order. With that in mind, they would be stuck with inventory they ordered for you (basicly a special order). If its a high ticket item, or a difficult to sell item, I would not be surprised by a restock charge in that event. But, I would expect the retailer to disclose that either at the time of the sale or as part of their stated return policy. Its likely that this preorder is considered a special order.
Pre-orders exist to protect the manufacturer/importer from being stuck with inventory should the project not sell. I don't like pre-orders, but nothing is wrong with this concept.
Retailers, routinely commit to purchasing product with no guarantee that the product will sell. Sometimes it sells out, sometimes the retailer gets stuck with unsold inventory. That's a risk and cost of being in business.
Re-stock charges were invented to protect the retailer from frivolous shoppers, who routinely buy, try, (wear once) and return product, and in some cases shoplifters who steal, then return items to get cash. (Common practice locally). This is a reasonable practice for return items.
Re-stocking fees for orders not filled and cancelled are not acceptable. If the product is not delivered,there is nothing to re-stock, therefore no justification for a restocking fee, no matter how much the retailer whines.
Until the product is actually delivered and available for sale, it doesn't exist.
I had a similar issue with a Big Box home center; and the Credit Card company and County Consumer Affairs Department, all agreed with me that they (BB Home Center), cannot charge a re-stocking fee, for an order not delivered within a reasonable time - even "special orders" - after pre-paid purchase. Once the delivery is accepted, the circumstance changes. Ultimately, the BB Home Center refunded the (frivolous) charge.
Remember, the recent well publicized incident with the Canadian Retailer, that required customers make deposits for pre-orders, then disappeared from the face of the earth; sticking not only the consumers, but also the manufacturer/importer(s). If it wasn't for the good will of other business concerns, the consumers who made deposits or pre-paid would have had no recourse but to eat the loss.
Keep in mind the OP. Had the product been delivered within the promised time, there would have been no cancellation this discussion would not be happening.