3D video cards are a commodity, too, these days. Even they could offer open-source reference drivers that allow for full basic utilization of the hardware, albeit at suboptimal performance. The heavily-optimized trade secret like cool codepaths could be offered in binary drivers for those who want the last drop of perf.
The business problem of open source 3D drivers lies not so much in secret know-how in the drivers but in this: http://steveblank.com/2009/04/16/supermac-war-story-7-buildi... High-end graphics cards tend to be exactly same as consumer level cards, save for few bits in some configuration memory that is used by driver to disable more advanced features/reduce performance.
It is. Making a new chip is very very expensive, but copying it is cheap. People demand millions of low end systems but only thousands of high end.
What companies do is use mass production for lowering the price not only of their low-end chips but high end too. They just disable and don't test the "advanced features" in low end cards.
With drivers you could enable it. Some blocks could be damaged(as it was not tested) but as a much lower price you just can buy new cheap ones.
It is relevant; people are "softmodding" GeForces into Quadros, theoretically costing Nvidia millions in revenue. Open-source drivers might make this even easier.