Since we do not see what questions are not published, it is impossible to determine if Hub Pages is being too conservative. Since the internet can be viewed by anyone, Hub Pages, like any website has to be concerned about youthful viewers.
Next, and I do not know this to be a fact, Google may have imposed some rules, even though Google's own safety check are designed to prevent minors from viewing adult material.
Thirdly, as one person stated, it might just be the manner in which the question is worded. If a slang term, even one commonly used, is used in place of an actual term, it might trigger the pull alarm. However, as i stated at the beginning, since most of us never see those questions, we do not know if Hub Pages is being too conservative in their decision to pull some questions.
Hub Pages and I have had our disagreements over the past year and i usually abide by their demands. They own the site. We are all basically guests, since we pay no membership fee.