Not necessarily so. As I said, my experience may not be representative of the most common workflows, but in the company I'm working for people often work on experimental or tangential stuff but at the same time they want their changes to keep pace with the work on the main line. I that case they can't afford to sully the trunk and at the same time, because merging back a branch is a major pain, they can't fork off a branch, unless it is a significant enough chunk of functionality or code they are changing. No amount of "collaboration management" is going to make the situation any better, because all options result in some amount of pain for someone, pain makes people touchy, and touchiness makes people not work together properly.

Just as you believe that a proper social structure and sufficiently clear conventions can overcome deficiencies in software, I believe the oposite - the capabilities and limitations of software can enforce certain patterns of behavior. And in my experience DVCSs end up having more of a positive effect on the development process.