Well, I'd draw the distinction between religiosity and spirituality. The former is associated with structured, formal religion: the Catholic that goes to Mass, the Orthodox Jew observing the sabbath and eating kosher, etc. But spirituality encompasses anything as vague as the notion that "there's some sort of higher power." When you're speaking about something that nebulous, it's very difficult to tell whether someone holds any such beliefs, and how much it means to them. More pointedly, I think it's quite easy to underestimate.