Yes, if this is so then I agree that open sourcing these drivers is harder. Though, SGI also has a history of supporting open source, so maybe its possible to convince them.
Still, nVidia can and should release the specs for their cards so that people can write better programs for them. For instance nvtv has problems with GF4 and FX cards, just beacuse the specs arent released.
"Never bump a baby carriage out of a crosswalk unless the kid's really asking for it."