It might start out as a tiny percentage, but all it takes is one person setting it up and letting the world know about it. Then pretty soon the WSJ is faced with millions of people getting free content again. They're complaining about people accessing their articles via a Google search and then clearing cookies to reset their counters. That's hardly mainstream; browsers have been burying the clear-cookies functionality deeper and deeper over the years because it's seen as an advanced-user-only kind of thing. And yet the WSJ has millions of people doing it, enough to make an impact on their bottom line.