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Hi,
Yes, it always has been different.
As AutoCAD for Mac is native Mac application, it has Mac-look user interface. Or at least, AutoCAD for Mac developers tried to make the application UI corresponding to the operating system.
There are also other differences between PC and Mac version of AutoCAD, you can read more about them here:
http://www.autodesk.com/products/autocad/compare/compare-platformsMaxim
