By your reasoning, these questions should then exist in at least 2 flavours:

- [How do I save a file in a directory that does not yet exist?](http://vi.stackexchange.com/q/678/51); we could use shell commands for this (`mkdir -p`), which are OS-specific.
- [How can I copy text to the system clipboard from Vim?](http://vi.stackexchange.com/q/84/51); there are some small differences in how clipboards work on different systems.
- [What's the simplest way to strip trailing whitespace from all lines in a file?](http://vi.stackexchange.com/q/454/51); we could use `sed`.
- [How to generate random numbers?](http://vi.stackexchange.com/q/807/51); there are some OS-specific solutions, but many more non-OS specific.
- [How to replace tabs with spaces?](http://vi.stackexchange.com/q/495/51); you can use `expand` and `unexpand`.
- ... etc.

These questions all have 1 or 2 OS-specific solutions. In some cases, they're even the *best* solutions, but I don't see how adding OS-specific tags is going to help. How would you imagine this, exactly?

- How to add line numbers in Vim only
- How to add line numbers in Linux
- How to add line numbers in MS Windows?
- How to add line numbers in a POSIX UNIX way?
- How to add line numbers in VMS?
- ... etc.

The Vimscript solution would also be a good answer to any of the other questions, and the Linux/UNIX answer could also be applicable to Windows. This would lead to a horrible fragmentation of answers.

Point in case: in the original line number question there are 3 Vim-only answers, and one UNIX-y answer. In your question, there are 2 (different) Vim-only answers, and one UNIX-y answer that is the same as the answer on the original question.  
How does this serve anyone? Now, *anyone* (UNIX and Windows users alike) will be served by coming across either question, *but* they are missing out on 2 or more answers which may work better in their case, because they don't know there is *another* question to look at!

So, what I did was:

- Vote to close your question as a duplicate
- Remove the [tag:microsoft-windows] tag from the original question (perhaps the question body could also be edited slightly to make it more generic)

Problem solved. The original question is now open to *all* sorts answers. 


Examples of questions where an OS-specific tag *is* useful:

- [How do I edit crontab files with Vim (I get the error: 'temp file must be edited in place')](http://vi.stackexchange.com/q/137/51); this is a specific problem with a specific error that only occurs on FreeBSD (and not Linux, for example)
- [How to edit content from the standard input?](http://vi.stackexchange.com/q/737/51); the question itself assumes UNIX concepts, and while these are also present on other systems (such as Windows), very few people use them in this manner (if it's even possible, not sure).
- [Can visual select mode be integrated with the Unix selection clipboard?](https://vi.stackexchange.com/questions/769/can-visual-select-mode-be-integrated-with-the-unix-selection-clipboard); seems obvious, Windows doesn't have a copy-on-select clipboard.

Furthermore, I'm also not sure of tagging a question with *both* [tag:unix] and [tag:linux] is necessarily good idea. I think that *all* of the [tag:linux] questions could just be tagged as [tag:unix], this is not a Linux-specific issue, but rather about  the UNIX version of Vim (`:echo has('unix')`). For the same reason, I would say that [tag:x11] is sometimes more appropriate than [tag:unix] (such as the "Can visual select mode be integrated with the Unix selection clipboard?" question).