just to be clear, MSDN does not specify WORLDVIEW because you can use any semantic name you want. WORLDVIEW is not a system value. you could have named it WV, or WORLDVIEWMATRIX if you wanted, as long as you have matching names in both the input layout and shader parameters
you could even use POS instead of POSITION, or TEXTURECOORDINATE instead of the common TEXCOORD if you wanted. system values (SV_) are values the non-programmable stages of the graphics pipeline such as the rasterizer stage can supply or take in. These are all documented on MSDN as you've seen.
I don't know why microsoft doesn't mention that you can change the semantic name as long as its not a system value, but i'm guessing its to keep things standard