1. Nvidia cards with driver before the 5X Series refuse to work with DX9c or better there are some bugs within ( in 3D modellers you are unable to select a single vertex and other similar things ), that will force you to update.
2. Not all mainstream cards support OpenGL, or better their drivers don't do! SiS, S3 and intels non-extreme chipset are only for office and not for 3d stuff and so don't even have full DX7 support nor do they have OpenGL support.
Other cards like NVidias, ATI and Intel Extreme need more recent drivers ( there are people with NV 4X drivers and similar ... 2 years and older drivers ), as their old drivers were not optimized for OpenGL, so the difference is quite large between old drivers and new drivers.
2. Not all mainstream cards support OpenGL, or better their drivers don't do! SiS, S3 and intels non-extreme chipset are only for office and not for 3d stuff and so don't even have full DX7 support nor do they have OpenGL support.
Other cards like NVidias, ATI and Intel Extreme need more recent drivers ( there are people with NV 4X drivers and similar ... 2 years and older drivers ), as their old drivers were not optimized for OpenGL, so the difference is quite large between old drivers and new drivers.