Dedicated as it is to “commentary on the production and distribution of economic ideas,” Economic Principals paused at the news last week that Leonard Riggio, founder and chairman of Barnes & Noble, Inc., plans to retire this autumn. He is 75. I wrote an article about Riggio in 1974, three years after he bought the hundred-year-old old Barnes & Noble Book Store a few blocks down the street from the Greenwich Village magazine offices where I worked. He had maxed-out credit card and finance company borrowings sufficient to swing a $1.2 million bank loan (those were the days before credit…