With one notable exception, the firms that make up what we know as Wall Street have always been part of an inbred, insular culture that most people only vaguely understand. The exception was Merrill Lynch, a firm that revolutionized the stock market by bringing Wall Street to Main Street, setting up offices in far-flung cities and towns long ignored by the giants of finance. With its "thundering herd" of financial advisers, perhaps no other business, whether in financial services or elsewhere, so...