I think you should read that as: "Which countries have laws which allow border inspectors to demand usernames/passwords to online services?" Those which do demand it are a subset of those which can demand it.

Your sovereignty argument is such an extreme interpretation of the question that it's almost certainly not what plg had in mind - if plg did have it in mind, then I find it hard to believe that question would have been asked in the first place.

Consider the question "what countries on border entry can draw and quarter entering citizens?" Your viewpoint seems to be that the correct answer is "all of them", yes?