Assuming the pricing model hasn't changed too much in the last decade or so...
Wholesale/Distribution costs will be about 52% of list price. That equates to a 48% discount from list price. To acquire that discount level, you just need to purchase sufficient quantity.
Amazon is able to buy that quantity! Barnes & Noble is also able to buy that quantity. Most small game shops are not able to buy that quantity.
Most small game shops need to go to a distributor that buys in quantity and then sells to smaller companies that have a smaller customer base. The distribution channel provides a valuable service. Without the distribution channel, most small stores wouldn't even be able to sell the books without having a distribution channel. Who would they buy it from?
See, it isn't in WotC's interests to sell small quantities. That is not their core business. Sure, it would be nice if WotC would be able to sell at wholesale prices to non-wholesale customers. At least, in theory. But that would require that they create an entire sales division to manage customer relationships. They would need to increase their shipping division to handle a large quantity of small shipments. They would increase their operating expenses, and that would increase the price of the books.
If WotC were going to go that route, they would need to seriously consider selling directly to the customer and cutting out all the middlemen. That way, they could eliminate all the discount structures and support the sales & shipping organizations without increasing the price of the books.
Of course, that would pretty much eliminate any discounting to the customer. It would kill a lot of the local gaming stores. WotC would be managing the game channel at that point. There would be a lot of moaning and groaning that it was now a price-fixed monopoly. Other games would have even less shelf space since there would be fewer shelves.
It would be a bad thing for the hobby in general I think.
Crack down on Amazon? WotC could cut them off as a customer I suppose. Not sell to them at all? Can you do that? Can you tell a company that you won't sell to them because their business model works and they are able to undercut the prices of their competitors? Can you do that, legally? WotC couldn't tell Amazon that they have to sell at a specific price. So, how do you crack down on Amazon for being successful at what they do?
I suppose the alternative is to stop selling in the book trade at all. Pull back on that distribution channel and only sell through the distribution trade channels. Of course, that runs counter to trying to get the game on more mainstream shelves. If WotC wants to sell to Barnes & Noble and other bookstores, they need to keep selling to Amazon. Amazon is successful at what they do and it puts a big squeeze on the local gaming store. Capitalism at work.
If game stores want to compete, they need to offer services that bring in customers that Amazon cannot offer. That is the best way to compete. It isn't always about price. Good service can still win. But if you want to compete with Amazon in terms of price only, you have a tough battle before you.