When B&N made this decision, they did it out of the principle of having the same titles available both in print and digital. They have a huge ebookstore with a significant chunk of the US ebook market, and there is some sense in defending it this way. By refusing the books, B&n struck back at their strongest competitor. It's only a moral victory, but it is still a victory.
BAM, on the other hand, doesn't have an ebookstore worth mentioning. BAM is not one of the big 4 US ebookstores (Kindle, Nook, iBooks, Kobo); they are one of the many that when combined make up about 5% of the market. What's more, BAM doesn't even sell their own ereader; they sell the Nook.
BAM has no ebookstore to defend, so there's not much of reason to decline Amazon's books. This move looks more like a general cluelessness than a principled stand. It's also coming from less than healthy company, and I suppose that we might now know why BAM has been losing money these past several years.