It may also be that the audience hasn't had enough time to internalize your material in a way that leads them to even have questions. People who are interested in your area may have to go home, find a copy of your paper, and study it heavily before they can even formulate a question. I always work, when I'm session chair, to develop at least one or two questions to seed the Q&A part of each talk and try prompt some discussion. Even if my questions are kind of lame, they may spark some ideas in others (as well may your answer!).