The point of using “DX10 HW” (or mentioning DX shader version) is to easily indicate that you are talking about HW which has some set of features required by that DX/shader version. I really wish people would stop referring to certain video cards are “DX10” hardware. This is not that much distinct from OGL situation if you wish to use OGL2.0 API features and still be able to run on OGL1.5 DX10 one used in common code and optional DX10.1 used where DX10.1 specific features are needed.

If you wish to be compatible with DX10 on pre-SP1 Vista and still use DX10.1 features with SP1, you will need to remember two device pointers. You got new guaranteed API features (GLSL) however you have no guarantee that they will be HW accelerated (which in DX world means they are unsupported).

This is very similar to increase of OGL version say from 1.5 to 2.0.

In that case the new functions will fail and some newly guaranteed things might be unavailable (You can query value containing level of HW support to determine if new features are supported). I would recommend to read DX documentation before commenting on this issue.

Directx opengl in windows 10