Currently, the excerpt for mac explicitly mentions OS X (as opposed to older operating systems to the mac). I agree with this definition since in common usage, "Mac" does indeed refer to OS X. But I think that in that case we should make osx be a synonym of mac.
Alternatively, if we want to make a stronger distinction between the operating system family and the current version, we can leave both tags but explicitly explain in the wiki for mac that it refers to the whole family, not just OS X. Additionally, since practically all mac questions are referring to a game running on OS X, if we do this we should probably change the tag from mac to osx on most existing mac questions.