I'd have to agree with Mark on this.
Why would you assume that open source developers aren't professional? As someone who as seen over 2 decades of programing (and more then that of source code) I can assure you that Open source code is generally much more cleaner and easier to understand the proprietary. It is obvious to me that you haven't ever done any Open Source programming or you would know better.
It's never a question about professionalism. Open Source developers (like myself) develop software when "time" permits and when I feel like it (unless I'm hired).
When I do write the software, I make sure it meets professional standards, but NVidia cannot place the vitality of its market share and customer satisfaction on the hopes that developers write unified drivers with a solid design paradigm that is compatiblie with NVidia standards and their release cycle.
Thus far, NVidia has provided exceptional support for Linux. My laptop has an ATI mobile chip and let's not dwell into the nightmares of finding "open source" drivers for it.
Just my 2c.