I seem to recall rumors that Starcraft 2 looked better when using DirectX 10 over DirectX 9. Is this true, and if so can you give examples (preferably in screenshot form)?
As far as I know, StarCraft II quality is not increased by using DirectX 10 as opposed to DirectX 9. I think XP users can crank up all settings to ultra as well.
Maybe the reason for that rumor is a Blizzard FAQ from 2007 (emphasis mine):
The official recommended system requirements, by the way, implicitly say DX10 is needed:
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: