The results aren't exactly a surprise given the Nouveau conditions... The Nouveau driver generally supports the GeForce 8/9 "NV50" hardware the best although there are exceptions. For the GeForce 9800GTX performing so well, it's one of the few graphics cards that could actually re-clock correctly and run stable through the OpenGL benchmarks without crashing. For the modern GeForce 400/500/600 Fermi and Kepler graphics cards, re-clocking is still a ways out so performance will be quite poor there for the foreseeable future.
It's too bad that after all these years the Nouveau driver is still struggling to properly support hardware from the GeForce 8 era.
Again, given the conditions, these results are in line with expectations.