Actually 4 developers, a fraction of a manager and no lawyers but don't let me slow you down
IIRC the main differences between radeon and nouveau in terms of performance progress are :
1. the NVidia hardware equivalent of two performance improving features (what we call tiling and HyperZ) are implemented in such a way that "turning them on" requires less driver work than doing the same on ATI/AMD hardware. Jerome and others been making great progress here recently.
2. the VLIW shader core probably requires relatively more shader compiler effort to get to comparable levels of HW utilization. I'm not sure this is an issue but we should know more once the SI open source driver starts to run beneficially.