I know but even though various shader iterations may be "standards," you always read about shaders not working on cards that support the given shader number. I'm always wary of standards and relying on them to work flawlessly across the board. Both card A and card B may support Shader 2.0 but certain 2.0 shaders may or may not work 100% correctly on both cards (or others). I think it mainly comes down to Nvidia vs. ATI implementation issues. A shader might work fine on an Nvidia card but crap out on an ATI card that should support it.