The abrupt resignation this week of William Lynch, the 43-year-old Barnes & Noble chief executive, was only the latest in a catalogue of troubles at one of the US's biggest book chains. If this were a business whodunnit, nobody could fail to spot the culprit: Amazon. Still, with bookshops everywhere in retreat as the internet takes an ever greater slice of their trade, it seemed to many that a chain with its own dedicated e-reader – the Nook – could have the answer. But with Barnes & Noble's device struggling to make any headway against Amazon's Kindle, that strategy, and...