By Diane Bartz WASHINGTON (Reuters) – The U.S. governments unwillingness to stop Amazon.com from using hardball tactics in fights with book publishers has angered book lovers but antitrust experts say regulators are unlikely to intervene in what appear to be business disputes. Amazon has delayed the delivery of some Hachette Book Group titles and even removed an option to pre-order The Silkworm, by Harry Potter author J.K. Rowling writing as Robert Galbraith. Some Amazon customers have gone public about their decision to buy books elsewhere. Advocates for authors and publishers use words like bullying and thuggish, and pine for government intervention.