I think, it's all about ambience - if it's good, it's fun to present something and a lot of people will do it. If it's not, it's rather unpleasant, so people will remain silent. Of course it helps to have a fire and things like this and if there are people that can presend something ad hoc to break the ice for others as was the guitar presentation at dc13. 15 felt like "don't let me be the first one speaking up" ;)