Our top three tags:
Each of those three arguably has some kind of more meaningful version breakdown, and are in effect meta-tags defining which world the question resides in and depends on other tags being present to actually define the question's domain.
Windows has a whole constellation of tags. Apache has three major versions. Linux is the tricky one, and it may be justified in keeping it as a stand-alone even if we do break up Windows and Apache.
Do we want to mass-untag windows and then go through the untagged posts to clean up the remainders? That's 4500+ questions that'll get touched, and a certain unknown percentage will end up as untagged as windows is the only tag on it. This will be a major undertaking, and anyone with 500-rep or more can participate.
The Developers will have to do the mass untag, which will remove
windows from all 4500 questions. Everyone else comes in afterwards to retag the untagged questions that will result.