Although that Salesforce1 indeed spans more then just the mobile app, more then 90% of the questions that are posted around Salesforce1 are about the actual mobile app.
Lately, it happens more and more that questions are linked to the Salesforce1 tag while it is not related to the mobile app at all. But given the current tag wiki and also just the overall ambiguity around Salesforce1 as a term, I can see why some people would also link their question so Salesforce1.
It would be my suggestion that the existing Salesforce1 tag is renamed to (for example) Salesforce1-app . Or at least to something making it clear that the tag is to be used for the Salesforce1 mobile app.
For Salesforce1, I think that is really to broad to be a tag since it's more the new branding and way of thinking at Salesforce.