In 2005, when Silicon Valley entrepreneur Michael Arrington started TechCrunch, his popular blog on Internet startups, he saw it mainly as a chance to indulge his obsession with young technology companies. But it turned out that Arrington had latched onto something big. TechCrunch became the go-to site for the scoop on new Web companies. And, as technophiles flocked to TechCrunch, advertisers...