While everyone was discussing Barnes & Noble‘s acquisition of Fictionwise at the end of last week (see this MobyLives report, or this Wall St. Journal report from Jeffrey A. Trachtenberg), Amazon quietly made a statement of its own to its biggest competitor: As a Shelf Awareness report by John Mutter noted, the company “made a move by unveiling a service yesterday allowing customers to trade in used videogames for store credit on any Amazon offerings. This initiative is seen by many observers as a major threat to GameStop Corp., which was owned by B&N chairman Len Riggio and B&N before its IPO. He remains a director and chair of the executive committee.” So, on a day when most of the press was hailing B&N for what was widely seen as a wise move in the Fictionwise acqusition, how big a slap was this to Riggio? As Mutter astutely noted, “GameStop shares dropped 14%.”