All the talk of consolidation in the online brokerage industry has become reality. According to Merrill Lynch analysts, four leading firms form something of an oligopoly in the industry, accounting for about 80 percent of the industry's assets. The big four--Charles Schwab, Fidelity, E*Trade and Ameritrade--will only get bigger, most likely via acquisitions. The industry remains focused on growing assets and reducing their dependence on commissions. While the big four's future is no longer in doubt, there are some long-term questions. The business model issues that have dogged it for so long have not entirely gone away.

> Here's a MarketWatch article.