I'm torn between the fact that there really is a meaningly difference in the taxonomy here (and at least historically, it was relevant to this site) and the obvious issue that people suck at picking appropriate tags.
I think the solution is probably to make it harder for people to use the wrong tags without having the correct ones put in front of them. For example a mac could be made as a synonym of osx to catch people that start to type and don't know where to start. This way the first tag suggested to them when they start typing
ma... will be the tag most likely to be correct. Additionally the macintosh tag excerpt could be expanded with a blatant explanation/warning of what hardware is covered by that moniker. Currently reading what comes up in the popup won't tip off most people about how to use it.
Additionally the tag summary for osx would benefit from being simplified so people aren't so shy of using it.