I'm of the opinion we have whichever master tag works best for us / is used the most here / etc and just create synonyms for anything that falls in to the situation you are describing (only if a synonym is relevant and correct, of course).

In fact, if you look at the [synonyms][1] for [tag:microsoft-word] and you'll see that [tag:msword] is already a synonym, so really we are already using the same tag as SO.

Further to this, check out the [synonyms][2] for [msword] on SO - and you'll see they have [tag:microsoft-word] as a synonym already. 

Both sites already have the same tag group in place, so I don't see a real issue, and any other tags that could do with a similar grouping just need synonyms creating.

## Update
I just added `msword` for all sites on to my tag set, and was getting both SO [msword] questions and SU [tag:msword] question in the feed. So it seems to be doing the job it should be doing.

[msword]: https://stackoverflow.com/tags/msword
[1]: https://superuser.com/tags/microsoft-word/synonyms
[2]: https://stackoverflow.com/tags/msword/synonyms