St. Martin's is a Macmillan publisher, which is an Agency Model publishing house. The Amazon page says, "This price was set by the publisher".
To answer your question, B&N has repeatedly said that they don't price-match. At the same time, they often do just happen to match after a discrepancy is called to their attention.
BN.com doesn't do much over the weekend. Check back tomorrow and see if the price has been updated.
St. Martin's is an agency publisher (oops, saw that it was already pointed out). I did a quick search and that book is listed as $7.99 at every bookseller except Amazon, so it looks like it may be Amazon's mistake.