For goodness sakes guys...
DirectX is a LIBRARY
Thus is is a collection of various parts
If you go into
C:\Windows\System32
And look for d3dx9_ d3dx10_ d3dx11_ DLLs
You will then understand why you have them all side by side...
End Of! for heavens sake...
An Analogy would be you putting Leaded, un-Leaded, or Diesel in your car... one works with a different type of engine... thus depending on the application, its requirements change... if you notice when you change between engines inside some apps/games you have to exit and restart that application, this is to restart that engine...
hope this clears it up, man I would have thought most of you would know this... I am shocked !!! oh well... looksie -->