They say that, with as many used-book stores as there are, many have closed in the last 20 years.  They say that the Internet, while it has helped them move inventory to far-flung customers, has also driven off-the-street business, and even regulars.  "Why should anyone go to a bookstore when they can order a book from the comfort of their desk and get it in a day?" asked Michael Thompson, who has owned Michael R. 