So I think that this seems to be an appropriate discussion to the site, until you actually know the answer. The answer itself actually has nothing to do with gaming and is more appropriate for Game-Dev or SO than here. Unfortunately, I don't think I can convince you that this question is inappropriate without first giving the answer.

DirectX10 has a demonstrably noticeable effect on Starcraft 2, unfortunately its not the sort of thing I can show you in a screenshot.

Starcraft 2 is one of the few games to have Pixel Shader 2.0 as a minimum requirement. For those of you unaware of what a Pixel Shader is, it is a programmable piece of the graphics pipeline that allows developer code to run on the GPU. These Pixel Shaders are usually used for such buzz words as: Phong Shading, Bump Mapping, Volumetric Shadows... but they're actually a lot more basic than that as they're actually your fragment rasterizers (OpenGL even calls these Fragment Shaders).

Now you may be thinking: Wait a sec, Pixel Shader 2.0 debut on DirectX 9, not 10. So why are we talking about it?

Since Stacraft requires Pixel Shader 2.0, more advanced effects provided in Pixel Shader 3.0 and 4.0 (DirectX 9c and 10 respectively) have to be reconstructed in Pixel Shader 2.0 and as a result have much poorer performance time (ie. slower) and will set back your frame rate. By comparison these artifacts provided in Pixel Shader 4.0 will run smoother. However, if you provide Pixel Shader 2.0 code to run on a Pixel Shader 4.0 you will actually see a decrease in performance as compared to native code.

So what does this mean for me as a Gamer?

Nothing. If you were a game developer or a graphics programmer this is a really interesting conversation about trade offs in performance as compared to user base, and how trying to satisfy everyone you can end up with a poorer overall product; but you don't care about any of that because this is a gaming website. Much the way a programmer doesn't care about trade offs in Monitors, he only cares about which one he's running on.

We've been kind of lax on the nature of questions we let into this site, and I think this really shows it. However, that is a topic more appropriate for Meta so I won't discuss it here.

So I think that this seems to be an appropriate discussion to the site until you actually know the answer. The answer itself actually has nothing to do with gaming and is more appropriate for Game-Dev or SO than here. Unfortunately, I don't think I can convince you that this question is inappropriate without first giving the answer.

DirectX 10 has a demonstrably noticeable effect on Starcraft 2, unfortunately, it's not the sort of thing I can show you in a screenshot.

Starcraft 2 is one of the few games to have Pixel Shader 2.0 as a minimum requirement. For those of you unaware of what a Pixel Shader is, it is a programmable piece of the graphics pipeline that allows developer code to run on the GPU. These Pixel Shaders are usually used for such buzzwords as: Phong Shading, Bump Mapping, Volumetric Shadows... but they're actually a lot more basic than that as they're actually your fragment rasterizers (OpenGL even calls these Fragment Shaders).

Now you may be thinking: Wait a sec, Pixel Shader 2.0 debuted on DirectX 9, not 10. So why are we talking about it?

Since Starcraft 2 requires Pixel Shader 2.0, more advanced effects provided in Pixel Shader 3.0 and 4.0 (DirectX 9c and 10, respectively) have to be reconstructed in Pixel Shader 2.0 and, as a result, have a much poorer performance time (i.e., are slower) and will set back your frame rate. By comparison, these artifacts provided in Pixel Shader 4.0 will run smoother. However, if you provide Pixel Shader 2.0 code to run on Pixel Shader 4.0, you will actually see a decrease in performance as compared to native code.

So what does this mean for me as a Gamer?

Nothing. If you were a game developer or a graphics programmer, this is a really interesting conversation about trade-offs in performance as compared to the user base and how trying to satisfy everyone can end up with a poorer overall product, but you don't care about any of that because this is a gaming website. Much like a programmer doesn't care about trade-offs in monitors, he only cares about which one he's running on.