In an impassioned blog post, Rentzsch has explained his reasons for shuttering C4. He writes that Apple's insistence on top-down control over its platforms (presumably more the iPhone OS than the Mac) crushes innovation and makes developers overly reliant on Apple for moving technology forward.
Rentzsch explained, "By itself Section 3.3.1 wasn't enough to cause me to quit C4. I've weathered Apple lying to me and their never-ending series of autocratic App Store shenanigans." His link on 'lying to me' references the now-infamous Steve Jobs assertion that a rogue iPhone app could bring down Cingular's network.
The lack of community outrage to the 3.3.1 dictate (the portion of the iPhone OS 4.0 developer agreement that forbids third-party toolkits for app development) pushed him past the edge. "With resistance to Section 3.3.1 so scattershot and meek, it's become clear that I haven't made the impact I wanted with C4. It's also clear my interests and the Apple programming community's interests are farther apart than I had hoped."
C4 will be greatly missed. Responses to the conference's termination include this note from NetNewsWire dev Brent Simmons.