Why is it 'plundering' for B&N to print physical books, transport them to their brick-and-mortar stores to sell? There are real costs associated to doing so. It would not have zero cost for me to print and bind a copy myself at home.
If Amazon is going to sell public domain texts, then it would make sense to source them from PG, and fund some money from those sales to the non-profit, similarly, they could then funnel reports of typos to PG for review and correction (it was a bit of a struggle the last time I tried to get a text corrected, and the project founder/director actually stepped in on my behalf).