thank you for providing all the information, screenshots and test data.
I spent some time today in the try to understand the problem and came to the conclusion that you are saying that there is a difference when importing the same ESRI ASC file into Civil 3D - depending on the method. The difference is half a pixel.
Is this correct?
To check Civil 3D I did a test on my side and loaded the two test files for "corner" and "center" into Civil 3D.
I used the FDO connection, the point cloud and the import DEM functions.
After the import all data from the center file lined up and all data from the corner file lined up too.
Please see this screenvideo:
http://screencast.com/t/gGxOzlEs
Basically what happens is that you have a start coordinate pair (x,y) and then you tell the progam if this coordinate should be the center of a cell with size 1 in your case or if the coordinate should represent the lower left corner.
In conclusion from my point of view Civil 3D behaves as expected and it is exactly doing what you tell it to do.
Please let me know if this answers your question or if I did not understand you correctly.
Segnalibri