Sure, except they gave the presentations away for every year prior, and that apparently had no negative effect on attendance. That place was packed in 2010. I don't think holding back the presentation collateral is going to make people want to attend. In fact as you observed, unless holding it back somehow increases the quality of the collateral I might feel ripped off if I attended just to get the slides. All they need to do is have high profile presenters (like he kepler and Hubble guys) and people will come. FWIW those 2 talks plus RBA is why I went.