Would questions pertaining to the origins of, or reasons for, particular social practices or points of etiquette be on-topic? Examples might be of the "Why do we say "bless you" for a sneeze, but not a cough?"sort.
Understanding the history of practices and sayings can be helpful in our interpersonal skills, as it can help to have insight and understanding into why we do things, particularly for people who struggle.
There's nothing to say that topics surrounding interpersonal skills and practices are not on topic, we define the scope. This would include a great area of interest into the scope of the site.
I'm not for limiting the scope too much - yes broad questions, but not in issues surrounding interpersonal skills. It's a huge area that affects our lives daily and there's much to explore in it's depth and breadth.
Personally I'd really enjoy to have this as part of our scope.