Loss leaders are not isolated to a class product but rather are used to entice people into the store and while there it is hoped that they will find additional items to buy at full price. Amazon uses this technique on just about every item. You find this in play when you scroll down on your item and see, " What others have also bought when purchasing this item."
Personally, I use Amazon "loss leaders" to buy many items for photography and save hundreds of $$. Good example are filters. Normally lens filters will cost between $25-$100. Buying them when they run a ,loss leader, I can pay as little as $1.99 for a $50 filter. Having Amazon Prime, I also get free shipping on some of these. But these are true loss leaders and not a revenue class price policy. I can't tell you that a Tiffen soft effects #3 filter is $1.99 because yesterday I paid that. It was a loss leader that Amazon ran for the hour and I just happened to be there and get lucky. The books at $9.99 as the legal case is being made is a policy for a class of products that is consistent over time. It does not fit the retail definition of "loss leader"
Did Amazon sell books at $9.99 as a class policy or as a Loss leader? I don't know but if they did as a loss leader then I doubt a case for suit could be made. If they did this as a policy for all ebooks, similar to what is done for music on itunes without regard to titles then it is not a loss leader.
Gross profit vs. net profit. Gross Profit is unimportant except to academics. Remember the college professor in "Back To School"? Dangerfield wrote the academic's text book definition a whole new chapter in business in less than 2 minutes while other students took notes. Gross profit is for academics. Net profit is what matters in your pocket and in real world business. When we talk profits in business we always understand it is net profit. The question was how much was made, not what the gross profit was. The answer for one who understands business is No.
Personally, I feel a retailer should be able to sell any of their inventory they own for any price they want and suppliers should not be allowed to dictate MSRP as a rule for sales. Only exception to this is when the inventory is not owned by the retailer. This inventory is normally considered to be floor planned or delayed payment to the supplier or a lender. A retailer who sells a floorplanned item at a loss is forcing that loss on the at risk lender of the item. The inventory exists as collateral.