Ubuntu, the Linux distribution which tops the charts these days, is developed using this closed system. Kind of a contradiction in terms, one would think.
Read the comment at ITWire
The mind harks back to the BitKeeper affair. In 2002, Linus Torvalds decided to start using the BitKeeper source code management system for developing Linux. At that time, there was a commercial version and a free non-commercial version. The free version required that all change logs be sent to a world-readable server controlled by BitMover, the company that develops BitKeeper. Both were proprietary – no source provided.