Does Rupert Murdoch think he can double or even treble the number of visitors to WSJ.com if when he makes the site free? Don't be silly. He's much more ambitious than that:

Rupert Murdoch, the chairman of the News Corporation, said today that he intended to make access to The Wall Street Journal’s Web site free, trading subscription fees for anticipated ad revenue.
“We are studying it and we expect to make that free, and instead of having one million, having at least 10 million-15 million in every corner of the earth,” Mr. Murdoch said, referring to The Journal’s online readership.

This is entirely doable – although it will involve more than just removing the subscription firewall. At the moment the WSJ's website is atrociously designed, and a revolutionary (not evolutionary) soup-to-nuts redesign is long overdue. Murdoch definitely intends for the WSJ to compete with the NYT, it would be a great day for all internet users if wsj.com became as beautiful and easy to use as nytimes.com.