What to think of zero feedback at a conference
This is extremely common.  Usually the session chair will at least ask a question to be polite.  But...

I am certainly disappointed when I don't get any questions after a talk.  Indeed, my primary gauge of the success of a talk (by myself or someone else) is whether it provokes interesting questions.  Whenever I have listened to a really great talk, I've always had many questions afterward.

In my experience as a member of the audience, the most common reason that a speaker gets no questions is that the talk is too narrowly focused and does not contain enough motivation or context.  That is, the audience cannot digest the talk in relation to other things they know, so they cannot form meaningful questions.  

Thus the lack of questions is often a sign that you should spend more time on introductory material and present the meat of the talk at a higher level.  Often it is more effective to draw analogies and pictures or diagrams rather than to get lost in technical assumptions and extensive notation.  Your talk is an opportunity to advertise your research and provoke interest; it is certainly not reasonable to expect the audience to digest the details of your methods or results in 15 minutes or even an hour.  Yet most scientific talks still try to do the latter.  I believe this is why so many conference sessions are almost devoid of questions.