[peterwwillis]

Every year that some controversial BH talk happens that exposes some company's unpatched security vulnerabilities (or even questions the company's integrity), either the talk is pulled, or the talk materials are literally ripped out of the books or CDROMs given to attendees. As soon as a company gets wind that a talk might catch them with their pants down they threaten to file suit and Black Hat pulls the talk.

The Black Hat conference is about promoting the security industry. DEFCON, on the other hand, is about promoting hacker culture. It's a lot more common to see 0-day talks at DEFCON because there's much less industry spotlight [and thus, fewer general business professionals that could get scared by some new attack being announced].