Glyfair
Explorer
The cost/profit margins on PDF versus a print book will never justify greater than a 50% sale price to me. Its pure greed, IMO.
However, it's not all about cost/profit margins. WotC has a lot of factors to consider.
One of the primary ones is avoiding making the PDF a more attractive purchase than the print product. Game stores will complain if the product is available more cheaply online, and they are important to WotC's market overall.
Also, the cost of the print products are based on large print runs. If sales on PDFs ever make a significant dent in print products, prices might have to increase because of smaller print runs (not that I think this is a big issue right now).
WotC has stated before that there market for sale PDFs is not those looking for a secondary product. It is for those who have a difficult time getting the books at affordable prices, or those who place great value on a PDF version. There stance may have shifted since then, but not very much.