No, they're not. They are only probable potential sales. They're more like dinner reservations at a restaurant. It's an indication that someone is definitely thinking about buying what is being offered, but they still may not do so.Preorders are sales so at the very least set a floor to sales, but not a ceiling.
I do pre-orders all the time on many different things.. My card does not get charged until around the actual ship date. And by then, I've tended to cancel about half of them.
"When you preorder on Amazon when does it charge?"
"When you pre-order a not-yet-released item on Amazon, you will not be charged immediately — instead, the card on file will be charged a few days before the item is released, typically when it ships or a few days prior to its shipping, depending on the item."
So pre-orders are good for getting a kinda sorta feel for an items possible floor to sales, but that's it.